Richard Mudhar

Skytec PRO 600 PA Amplifier repaired but bad design can’t be fixed

tl;dr – to fix the problem throw the Skytec Pro 600 away and buy something better before the Skytec blows your speakers again. Don’t buy Skytec, and if you have it throw it away before it fails on you.

Skytec is cheap rubbish made in China for kids who are wannabe DJs but have little money. This is not quality – I had to repair this amplifier because of a fundamental defect in the engineering design. These are fine for background music, say in a pub. They’ll go reasonably loud in a modest party setting ,say 30 people, but it’s rough, and it’s nasty. You’ll save on the amp and pay in bass drive units if you DJ with this at any scale 😉 And get a limiter if you can, but if you can afford that you won’t be down at the Skytec end of the market.

I made the dumb mistake of buying one of these used from Cash Converters for £30 a while back. I bought it purely on price, I wanted something basic for parties of about 30-50 people. I knew nothing about PA, but I figured a hifi amp wouldn’t cut it for that sort of usage. What I hadn’t anticipated was people shift junk onto the PA market with design defects that were solved in the 1970s. They don’t even need any new parts, just put the Vbe multiplier on the heatsink rather than on the circuit board.

Skytec 600s are sold as 600W and the manual claims 600W output. They are absolutely away with the fairies on that, to the extent they should be done under the Trade Descriptions Act. I guess they hide behind the fact they don’t say RMS power, so they probably mean peak power, though that’s still only 280W. I measured 80V p-p, which is about 28Vrms. Run that into 4Ω and you’ll get V²/R≈200W. Do that for any length of time and it will blow because of the inadequate heatsinking and bad thermal design.

about 80Vp-p (I am using 10x probes) into 6ohms, 130W per channel. Don’t do it for too long, though

HiFi tower talk glowingly about the MOSFETs

Skytec’s PA-600 gives you the extra power you need with exceptional bass. All sound components are co-ordinated carefully and captivate their longevity. The modern MOSFET transistors and extra large power transformers give great sound and dynamics. The high build quality makes it the ideal amplifier for tours and gigging. For use on stages, for DJs, monitoring, parties and conferences.

but there ain’t no MOSFETs in this, simply a pair of paralleled bipolar junction transistors in the complementary pair output stage, 2SA1941 and 2SC5198. Toshiba described the transistors as suitable for 75W amps, you have two in parallel so 150W tops, okay times two for stereo = 300W. The toroidal transformer isn’t over 600W, I’d guess 200W from the size.

It worked OK for me for a couple of years, but then I let someone use it unsupervised for live music. Which brings me to the first warning

Do NOT use the Skytec 600 for live music unless you are aware of the risks you are taking!

I wasn’t, there, and the result was a blown output stage and blown woofer. It only cost me £11 to service the amp and £50 to change out the woofer, so I am now down £91, and I still have a junk amplifier, though it works now. Now that I know the ghastly horror of the circuit design I am not sure I have the balls to use it again, but at least it works as it was meant to originally 😉

Why not for live music then?

After all, the promotional blurb says this:

The high build quality makes it the ideal amplifier for tours and gigging. For use on stages, for DJs, monitoring, parties and conferences.

so what’s the problems then? Dynamic range – live music has a higher peak to mean ratio than recorded music. You end up pushing the bugger harder, so unless you limit the live source in the mix you’ll clip the output. At least that’s what I assume happened, I wasn’t there when It failed 😉 The Skytec is fine for prerecorded music, but the basic problem is that this amp has zero protection for the speakers or the output stage. Worse still, the VBE multiplier that biases the output stage isn’t thermally coupled to the heatsink on the output stage. Let’s hear it from Rod Elliott why this sucks

Thermal Stability

It can be seen that in the Darlington configuration, there are two emitter-base junctions for each output device. Since each has its own thermal characteristic (a fall of about 2mV per degree C), the combination can be difficult to make thermally stable. In addition, the gain of transistors often increases as they get hotter, thus compounding the problem. The bias ‘servo’, typically a transistor Vbe multiplier, must be mounted on the heatsink to ensure good thermal equilibrium with the output devices, and in some cases can still barely manage to maintain thermal stability.

If stability is not maintained, the amplifier may be subject to thermal runaway, where after a certain output device temperature is reached, the continued fall of Vbe causes even more quiescent current to flow, causing the temperature to rise further, and so on. A point is reached where the power dissipated is so high that the output transistors fail – often with catastrophic results to the remainder of the circuit and/or the attached loudspeakers.

I got to find that out the hard way. I’ve actually managed to do a fair number of parties with this fine, but I was always careful to keep the bouncing LEDs of the output display under control by controlling the master gain.

How does the Skytec PRO600 do thermal stability?

On a wing and a prayer.

PC case fan blowing on the internal heatsink

They run a PC case fan 100% of the time onto the main heatsink, sucking air out of the case, inflow is through the front. There’s no margin for error – although I didn’t trace the circuit it’s a complementary pair of paralleled output transistors driven by a driver (effectively making a Darlington output) so you got four VBE drops reducing with temperature at 2mV/deg C, asking for thermal runaway. There’s no fight against that with the VBE multiplier because it’s not thermally coupled. Get the die temp of those output devices hot enough, say 40C above ambient and you have 40*2*2 = 160mV less bias than you started with (the drivers are conveniently mounted on the heatsink to make sure their VBE drops too). This is designed for thermal runaway and the only thing standing between you and a blown output stage is the hope the heatsink and the fan keep the temperature rise down. You can get a little bit of an idea of the architecture from this thread and this PDF of a similar noname PA amp which gives a rough idea of the architecture on the output

Schematic someone has traced out of a similar piece of junk. In my case the four o/p transistors are 2x 2SA1941 (BG7,8) and 2x 2SC5198 (BG 9,10). BG4 is the offending Vbe multiplier that isn’t on the heatsink.

How to fix a Skytec 600 blown output stage

Change the 2SA1941 and 2SC5198 transistors 😉 I buzzed these through with a DVM on diode setting and found them all short, traced back to the drivers expecting them to have gone but they were OK, traced back a further stage of BJTs but they were OK too. The 5A fuse saved the other passive components.

It’s quite repair-friendly – unscrew the three screws on the base holding the heatsink, unplug all the connectors after taking a photo to remember where they go back. Lift the PA module out, snip the duff transistor legs to save the PCB while desoldering the pins one at a time.

snipping the duff transistor legs lets you unsolder the legs one at a time, saving the PCB from overheating.

I powered up the repaired stage on a 30-0-30V bench power supply set to limit at 100mA, I know it’s meant to work off 60-0-60V but I got a signal through and confirmed it wasn’t still duff, before getting it onto the main supply. I also compared the quiescent current (10mA at 30-0-30V) with the good side, which was the same, so I figured the VBE multiplier was still set about right. Easy win for about £11 in parts. In fact one of the old output transistors was still okay, presumably saved by it’s parallel buddy shorting across it, but I’m not chancing it.

I also went round and tightened the output transistors a tad. It’s easy to overdo this, but the still- working side was about finger-tight like the failed side. I wonder if this also led to the early demise. You just can’t risk the transistor die heating up to any great amount with this design.

Having fixed it I started to test it looking for why it blew. I got a couple of 50W 6Ω wirewound resistors. These are sold on Ebay to people doing LED upgrades to their lights, to put in parallel with the LEDs and draw 24W so the automotive CAN bus filament blown detector doesn’t keep going off. I figured 6Ω is a nice compromise between typical 8Ω and 4Ω speaker loads; real speakers present complex loads anyway. It was the cheapest way of getting a power resistor up to the job. I then dunk the resistors in a pan of water.

since I don’t have a heatsink/fan combo up to dissipating 300W. I know electricity and water don’t really mix, but I figure the water isn’t going to shunt my 6 ohms too much. Worth heatshrinking the ends of the resistors though 😉 The reason I used a pan is because the failure mode of these type of power resistors is to violently eject the ceramic slug out the end. So a Pyrex dish or a jam jar isn’t really desirable.

Running both channels full tilt at 130Wpc for two minutes the transistors get up to about 50C at the hottest part of the plastic case. If fairness to the amp I’ve been able to fill a rented Scout hall with music without ever taking it up that high even on peaks, so I ran it for five minutes at 33 watts per channel (~40V p-p). And got the transistor cases up to 110C. The manufacturer’s spec for the junction temperature is 150C peak. If you thrash this like that for a long time I guess the heatsink/case fan combo is hopelessly inadequate, and it blows.

Sadly I battle tested the inadequacy of the design a second time. Five minutes after running the second test, after I had brought the signal down to 0, I was greeted with this, telling me the right hand channel has gone DC, presumably thermal runaway again.

While I know how to repair this, I don’t know how to fix it to make it fit for purpose because of the fact the Vbe multiplier isn’t on the heatsink. It’s probably true that my needs don’t push it that hard, but an amplifier that blows after running a steady 33W for five minutes isn’t something I’m going to risk ever using, so it’s time to scrap it.

Skytec Pro600 – Avoid. Just say no.

SoilBioLab course at Rushall Farm

Richard and Joanne went along to the one day course run by SoilBioLab at Rushall Farm late last year. Simon, Andrea and Jen from the SoilBioLab team taught us how to take soil samples and qualitatively grade soils and compost & compost tea.

Their approach to qualifying the results is quicker and (in our humble opinion) more applicable to fieldwork than the full Soil Food Web Elaine Ingham method. You can use a cheaper biological microscope, closer to the student microscope end of the scale, rather than the more sophisticated microscope recommended by Elaine Ingham in her video training courses.

We found it a really useful day. In theory we “knew” a lot of this stuff, but there is nothing more useful than spending the day with people who really know their stuff, which the SoilBioLab team most certainly do, and being able to ask dumb questions, which they were unfailingly able to answer.

Soil Biolab also offer more detailed quantitative tests if you send them soil samples by post – they suggest a combination of doing your own analysis along with getting them to do more in depth tests from time to time.

Freshly taken sample showing layers in soil

Simon demonstrating sampling in grassland

Andrea explaining soil micro-organisms, and how to identify them

SoilBioLab team member Jen was extremely helpful in explaining how to use a microscope & identify soil micro-organisms.

Guest post on Hot Composting from Dave Beecher

An enormous thank you to Dave Beecher this guest post on his experience of hot composting. Dave has been working alongside Zach Wright who himself learned directly from the mighty Elaine Ingham herself! This post includes a very entertaining video of Dave making his compost pile, an activity the clearly fascinated everyone (including Billy the Dog!) at Caerhys Organic Farm in St Davids, Wales! You can contact Dave on (an image to protect him from spam):

So, my first attempt only got as far as turn 3 and would not heat up after that. It became very wet (liquid running out the bottom) once all the green material started to break down. I didn’t have enough high N and my green material contained a lot of internal water.

Pile shrunk down a lot as I did not compact sufficiently when building the initial pile. Using a flat head shovel every 6-12 inches works well. The second pallet was larger than first allowing for a bigger ring and making the pile look really small. Keep the diameter of the ring the same regardless of pallet size. This will allow better control when turning as you will be able to divide you material up evenly to comply with the turning break down as shown below.

I started again and treated the first attempt as 50% and then added 20% brown, 20% green and 10% high N. This worked a treat and i ended up getting 6 turns in as it was still quiet hot after the 5th.

Temp
I used a 500kg grain bag with pull cord to cover the pile. This worked well as i could open the top and release excess heat and condensation, preventing the top of the pile from getting soggy. I had to turn two days in a row as it was getting very close to 70c. I made sure to air it out well on the second turn and not compact it down at all. This allowed me to keep the temp 55-59C for 3 days.

Water
After the first pile getting to wet i held back a little on the water when making the second pile. The temp was slow to rise only 18C the following morning. I add 7L of water to the top and sides that evening, it reached temp by the next day. I continued to add water when need and based it on visual and squeeze method.

Flies and Midges
When the pile was covered and slightly damp from condensation there were a few hanging around. Once i removed it and allowed it to dry out they disappeared

Mushroom
Got my first 2 mushroom on day 17 loads on day 19, by day 22 they were gone just some pin heads were visible.

Compost Biology
After 1 month i found 5 bacteria feeding nematodes, one predatory, lots of amoeba and one our two fungi spores

After 7 weeks i was getting 30-50 nematodes per slide mainly bacteria and 3-5 predatory, a diverse range of amoeba and fungi development.

The pile is now 10 weeks old, I will be heading back to Wales next week to see how it’s getting on and will let you.

Happy Composting!

Dave

How to make Biologically Active Compost Extract In 20 Days

An enormous thank you to Nigel Griffith for this guest post on Farm Scale Composting at Landews Meadow Regenerative Agriculture Center, Challock, Kent in the South East of England. It is full of incredibly helpful, practical advice!

At Landews Meadow one of our main goals is to improve and regenerate our soils.

Our farm is just under 56 acres of very open land on the top of the North Kent Downs, we can see the North Sea from one field and a short walk away and we can see the English channel, so we have a very exposed site. Our soil is a heavy clay with lots of flints in and 8 feet down you hit the chalk downs. The soil gets boggy in winter and bakes hard in the summer and suffers from compaction, wind erosion and water erosion. For the past 30 plus years the fields had been used for set stocking sheep or cut for hay. The previous management system had been spraying nitrogen fertilisers and weed killers on the pasture.

We have implemented systems (swales, keyline ploughing and tree planting) to reduce the run off, increase filtration and water retention and reduce wind burn. Our initial tests on the soil showed that whilst it has a good mineral content but the only soil biology to be found was bacterial. With only bacteria in soil it will become more compacted and more acidic.

For the past 2 years we have been researching and trialling compost and compost teas to find a workable solution to kick starting the life in our soil. As the vast majority of our livestock lives outside 365 days a year we don’t generate lots of soiled bedding so we don’t have vast supplies of materials for making compost.

In April of 2016 we attended a course with Zach Wright of www.livingsoil.net who is one of a very few people certified and approved by Elaine Ingham. Zach describes himself as a Decompiculturalist and has spent most of his adult life making compost. He has refined the process and his course taught us not just how to make quality compost, but how to make quality compost that was full of soil life and how to test it with a microscope.

In this blog I want to share with you the basics of making ‘Biologicaly alive beneficial compost’ and how we apply this to our land. Field trials conducted by Zach and Elaine and trials sponsored by The Duchy of Cornwall are starting to show huge benefits for both pasture and crops when the soil is brought back to life, this soil food web breaks down available matter in the soil, making the the nutrients soluble and available to the plant, so that no artificial fertilsers are required. Once you have re-established this lost biology in your soil all you have to ensure is that you are feeding the soil food web and not damaging it by pouring on chemicals, we feed our microbes with holistically grazed animals (Cattle, chickens and ducks), the cattle trample grass and manure and the chickens scrape and manure as they go providing food for the soil food web.

Tools required

Square mesh wire with 2 inch mesh, 4ft wide or higher
A pitch fork
A shovel
2 pallets
Some fine mesh or landscape cloth
A thermometer (12 inches long minimum)
A hose pipe

Raw Materials

The main constituent parts of any compost fit in to 3 categories:

High Nitrogen (Hot): Manure, Soiled hay bedding, used brewers grains, coffee grinds
Browns: Straw, Wood chips, leaves
Greens: grass cuttings, hay, green hedge cuttings, green kitchen waste

The more local diversity you can add the better, you are looking to create environments for a huge variety of microbial life. We do a walk around the farm and find other things to throw in, feathers, mushrooms (No shelf or conch type) and whatever else we can find that will decompose.

We also add ground seaweed meal and crushed up bio char.

The process

Put your fine mesh or cloth on your pallet then roll out your mesh in to a tube that will fit on top of the pallet (see pictures)
Collect sufficient quantities of all your 3 ingredients, this is the longest part of the process, we get wood chips delivered to site and save the small amounts of bedding or spoiled straw. We usually have to mow a lawn to get the greens or cut our hedge or reeds in the lake. A bale of hay soaked in water is our last (lazy) resort.
Building the Pile: Have all your materials placed in piles around your pallet and mesh, place a few forks of straw in the bottom to aid aeration then start adding materials in the ratio of 2 Browns, 2 Greens 1 Hot, work round the pile adding material, mix it all in, you want as much cross contact as possible and water well as you go.
Critical Tip : I had never seen as much water used before in building a pile, I was always under the impression you did not want water or it would become anaerobic, but Zach’s method you keep spraying the pile as you go and keep it all moist. To test the moisture level (when building and each day after) pull out a handful of material and squeeze it tightly, at the correct moisture level you should get a few drips of water coming out between your fingers, if you don’t get anything, it is too dry, if it is like wringing out a wet cloth then it is too wet.
Keep building, mixing and watering, adding your extra bits for diversity along the way until the mesh is full.

Your pile will be impacted by the elements depending on the time of year and its position, if it is exposed to rain and wind you may want to cover it with a tarp or it could get too dry or too wet, we leave ours open for the first few days to get the aeration of the wind but cover it if we are due torrential rain and after 7 days to stop it drying out.

Managing your Pile

Check both the moisture and temperature daily and record them in a table like this:

Nigel’s Record sheet (links to PDF version)

If your pile is too dry, water it, as soon as your pile is over 70 degrees it needs to be turned.

Work to this turning schedule

Temperature	Days Before Turn
55 – 59 degrees C	3 days
60- 65 degrees C	2 days
66 – 70 degrees C	1 day
Above 70 degrees C	TURN NOW

The target is to keep the pile between 55 degrees and 70 degrees with a minimum of 5 turns so every part of your pile has spent 3 days at the core. This will kill weed seeds and pathogens but allow your beneficials to grow and speeds up the decomposition of the matter . Lower than 55 degrees and pathogens and seeds can survive, above 70 degrees and you are killing everything.
Interestingly the UK regulations for commercial compost require PAS 100 compost to have been kept at a much higher temperature for much longer periods (understandable when they are cleansing all types of waste in their process) but we want our pile to be a breeding ground for our soil life so it is critical that as soon as you go above 70 degrees to turn it. Every commercial compost I have examined under the microscope is devoid of anything but bacteria.

The Turning Process

Top third goes on to a tarp on the floor
Middle (the hot steaming bit!) goes to the bottom
The top goes back in to make the sides (dig out a hole as best you can)
The sides go in to the middle
Bottom goes on the top.As you are turning the pile you are getting oxygen back in to it and you may need to wet it with your hose pipe. Mix it up as best you can as you go.Check you pile daily, note the temperatures and moisture and anything else , smell, insects fungi and turn and water as required.In under 20 days you should have a well decomposed pile. We examine our compost under the microscope to check we have the beneficials we were after and leave it under a tarp to continue decomposition for another month then start to use it in compost extract or tea.

Visit to Landews Meadow Farm in Kent

Last Tuesday Richard and Joanne headed down to Kent to visit Nigel and Wendy at Landews Meadow Farm who very kindly found some time in their very busy work schedule to show us round. Their farm is a truly impressive place, and I’ve written up a summary of the “non-compost” parts of what we learned on The Oak Tree Farm website here.

The lovely Nigel and Wendy of Landews Meadow Farm

Nigel has been working hard to implement Elaine Ingham’s methods on his farm, and the results are visible and impressive. He hasn’t carried out controlled tests as he is keen to have the benefits of the soil improvements everywhere, something we can understand, and have done ourselves with our 2016 tomato polytunnel, but the number of wormcasts on his pasture surface show very clearly that there is a lot of biology in his soil! Like us, his farm has very low rainfall, particularly in summer, though his soil is clay unlike the sandy loam of The Oak Tree.

One of countless worm casts at Landews Meadow Farm; and promising indicator of good soil life!

Nigel went on Zach Wright’s UK course Spring 2016. We were gutted to have missed this, it looked really excellent, but we understand that Dave Beecher has been working closely with Zach and will be running similar courses in the UK soon – when we hear more we’ll keep you posted!

Nigel and Joanne inspecting an "in progress" compost heap. The tarp used to cover and surround the heap has been pulled off so we could take a look. — Nigel and Joanne inspecting an “in progress” compost heap. The tarp used to cover and surround the heap has been pulled off so we could take a look.

Nigel makes compost in the “hardware cloth” cylinders recommended by both Zach Wright and Elaine Ingham. We’ve found that hardware cloth doesn’t seem to be a British English term, which makes it hard to track down to buy. “Galvanised wire mesh” seems to be similar stuff in the UK. Nigel builds his heaps on pallets covered with woven weed control fabric “mypex” and he wraps a single layer of tarp over and round the heap to keep the heat in.

Nigel’s raw ingredients are

40% green material (cut grass, or, slightly less successful, hay)
40% woodchip
20% nitrogenous stuff. He uses a cow poo mixed with water to a fairly runny consistency: he has plenty of the raw material to hand…

A fine member of the Landews Meadow Farm Herd, and source of nitrogenous manure!

He uses a hose with a finger over the end to spray materials as they are added to the heap (by contrast we have been using a fine spray head). He has had considerable success with this method, managing to match the exacting temperature profile demanded by Elaine Ingham and Zach Wright’s methods, and the resulting material certainly looks excellent.

Landews Meadow Farm is on quite an exposed site (they have a fine wind turbine!) and while the compost area is protected by a hedgerow, it takes a fair bit of incoming weather (the English Channel is visible from the farm on a clear day!) Clearly the use of animal manure slurry is a good way to get compost heaps up to temperature as we found with using poultry manure slurry in our heap 160910. We had struggled to get heaps up to temperature reliably before doing this. He does five compost heap turns, carefully manipulating the material to ensure that all parts get up to heat in the hot centre at some point.

We were particularly interested to hear the simple “Zach Wright” method of making compost extract. We had attempted to mimic this following a phone conversation with Nigel before the visit, but we had made it more complicated than it needed to be! Nigel simply takes a 30l container, adds compost to it (see the photo below for an idea of how much) and then stirs it with a stick for about 30 seconds. Easy!

The right sort of amount of compost to add to about 30l of water to make compost extract

Once stirred he uses the secret ingredient of a jelly bag (the sort you use to strain fruit to make sweet jelly preserves) to strain the mixture before using it in his tractor mounted sprayer – brilliant! It is just these sorts of practical details we wanted to learn – it had never occurred to me to use a jelly bag (though I have one in the loft somewhere!) He then dilutes it into about 200l of water. Apparently Zach Wright dilutes further saying that one hardware cloth/galvanised wire mesh heap can be used to treat 200 acres!

The Landews Meadow Farm tractor mounted sprayer (once again I have tractor envy!!!)

Once again, a huge thank you to Nigel and Wendy for welcoming us to their beautiful, innovative and productive farm!

A new way of making compost extract in smaller batches

Compost extract was a great success but it seems to take time to take effect. The effect on the sweetcorn was marginally noticeable with only a month and a half, whereas the beans were very noticeable the next year.

If this hypothesis is true (other differences are the crops were different, and the beans and tomatoes were in the polytunnels and the sweetcorn outside) then we need to really get the compost extract out now for next year.

The 160901 compost isn’t really ready, although it has fallen back to ambient temperature, so we chose to run the experiment to get ahead. This is much more bacterial than fungal under the microscope, which is to be expected as bacterial reproduction is so much faster. But needs must in this case.

We adopted a tip from Nigel of Landews Meadow Farm in Kent and trialled using about 0.5kg of compost stirred vigorously into about 40l of water in a trug. This is more economical with the compost than the method we used last year, so we can make more extract from a given amount of compost if it works, and it is more suited to our volumes for experimentation distributing by hand. The other method is more suited to bigger volumes and mechanical spraying, because the net curtain filter screens the particle size so it is less likely to clog pumps and nozzles.

The aim is to stir fast enough to establish a vortex in the water and occasionally reverse direction. Shades of Steiner’s biodynamics here, but also a good way to aerate a volume of water by hand.

Ben, visiting from Frith Farm CSA in Hull gave us a hand with stirring the extract

Continue reading “A new way of making compost extract in smaller batches”

Sonar ranger for the visually impaired

This project was for someone I know who is blind. If you can’t see your surrounds then coming into contact with things is always a surprise, she is elderly so it’s not easy to use a cane, which is the low-tech surprisingly effective way of orientating yourself if you can’t see.

the fisihed ranger - the glue stick on the side is to give a softwer contact and avoid damaging the ultrasonic sensors — the fisihed ranger – the glue stick on the side is to give a softwer contact and avoid damaging the ultrasonic sensors

Initially I thought the idea was original, but a little Googling shows it certainly isn’t and more sophisticated versions are available commercially, like the minigude and K sonar. But for the low cost ~ £15 of a PIC and a few bits it’s worth a go to see if the basic principle works, assistive tech seems very variable in effectiveness depending on the user.

Bats use ultrasonic pulses to locate things by emitting a pulse of high frequency sound and listening for the echo. More recently ultrasonic ranging has become a big thing in the robotics field. These modules turn the analogue interfacing into a microcontroller-friendly length of pulse digital signal. I bought a SR04 from ebay for less than £3, which does much of the hard work.

You apply 5V, pulse the trig for 10μs and get a pulse of varying duration from Echo. It’s surprising easy to turn that into a tone rising in frequency as you get closer. Start a timer on the leading edge of the echo return, and when the training edge comes, copy the count into the duration control of another timer (copy into the PICs CCP module which controls the period of TMR1) Then toggle a pin when the CCP module resets TMR1.

You have to do a little error checking to catch timeouts or when the distance is too large, the signal gets more reliable as you get closer to an object, which is good. I was able to find doors and follow a wall using it. It works better when the ultrasonic sensors are vertical, the beam spread is narrower. It does not help you find things on the floor.

I was surprised how little it takes to make one of these now – all you need is the HC04, a 16f628 and a piezo speaker, and it runs 5mA off a 9V battery regulated down to 5V.

PIC code on Github

This works better in real-world application held vertically, not horizontally. but I didn’t know that when I made the video.

Olympus LS10 and LS14 DIY wired remote control

tl;dr – the schematic

Olympus LS10 (and LS14) wired remote schematic

A new approach to a timed recorder

For the last year or so I’ve been trying to make an timed start recorder using a Raspberry Pi and the Wolfson/Cirrus audio card. I was able to make it work, but never eliminate some rattiness in terms of overruns on record – I confess I couldn’t hear them, but it didn’t give me a good feeling. Then I added up the costs –

£25 – Cirrus Audio card
£27 – Raspberry Pi B+£10 – case and odds and sods to make it work
£20 – PCB, time and bits to make a preamp to get from mic to line level

so I’m looking at £80 to get off the ground, and that gives me a seriously power-hungry SD audio recorder, although I can use a timer to save the power drain for active service.

Alternatively, if I could crack the remote control for them I could go on ebay and get a secondhand Olympus LS10, or one of the similar models (LS-5, LS-11, LS-12, LS-14) and use my own LS10 to start with. I can feed a mic straight into the LS10, no extra preamp required and the audio spec is good.

Reverse engineering the Olympus remote control protocol

This cost me £90 on ebay, and it turned out I didn’t need it. You get the info for free, but then I got a natty nearly new LS-14 with an RS30 remote control, so I’m not too unhappy. Unfortunately the RS30 doesn’t work with my Olympus LS10, don’t know why. I’d have been hacked off if I’d just got the RS30¹. Works a treat with the LS14 it came with, on their own a RS30 seems to go for £50, so I got an okay deal.

Google first – I owe dashanna of the naturerecordists’ list for inspiration, I vaguely recall seeing that post go through on the list. Their solution is this

1610_dashanna

The connector is an evil little 2.5mm four-pole jack, and these are a bear to solder

nasty connectors to solder, though easier when you realise you only need t wire to two parts. You can pick up 3.3V on the tip, which may be of use... — nasty connectors to solder, though easier when you realise you only need to wire two parts. You can pick up 3.3V on the tip, which may be of use…

I can’t help wondering if life would be easier using a three-pole jack, since only sleeve and ring are needed. Now I didn’t like that battery in dashanna’s version – I mean who the heck would make a wired remote for a machine offering you a 3.3V supply on the tip of the plug and demand you go fit a battery in your remote? It’s just not a clean engineering solution at all. But apparently it works.

So I rigged the cable in series with the RS30 and sniffed the signals. Of the TRRS the tip had 3.3V, the second ring seemed open circuit, the first ring had the wanted signal and the sleeve was ground. Presumably the IR receiver and LED driver are powered off the 3.3V on tip. The signal on the first ring rests high at 3.3V.

Record is this funny little signal, 100ms at about 1.5V followed by a low

Stop is this signal, pull to ground for 100ms

In practice you can ignore the second pulse. For all I know it could be an ack back to the receiver to light the LED. I tried using a couple of diodes to pull the signal down to 1.2V but that didn’t initialise record. I then figured this is one of those analogue resistor chain remotes, so I look for what resistor would give me ~1.5V. Turns out if you replace the 1.5V battery in dashanna’s schematic with 100k you get about 1.5V and the recorder starts recording. You don’t need the second pulse at all, and the debouncing seems to be done in the recorder, it takes a little while, up to about half a second to start recording. I guess that means inside the recorder there’s a 100k resistor to the 3.3V rail in series with the first ring.

That works with both the LS 10 and the new LS14, although the RS30 only works with the LS14. So now all I need do is mod the timer to pull down a couple of pins, one through 100k. If I make the stop command the open-drain pin to ring and the rec command a normal pin resting High via 100k to ring, and pull the relevant pin down for 100ms I should be good to go.

I’ve just got onto the Olympus RS30 website and if you scroll through the models that is compatible with it includes the LS-3, LS-5, LS-11, LS-12, LS14, LS-20M, LS100 so perhaps my LS10 was never compatible with it and Olympus have changed their mind since writing the LS10 manual which says on p65 “Exclusive remote control RS30W (scheduled for Spring 2008)” ↩

What I learned over a year of growing with Soil Biology

It’s been just over a year that I completed Elaine Ingham’s Life in the Soil classes. It seems a good time to take stock, as we go into the colder part of the year when practical fieldwork winds down. So what have I learned?

There is certainly promise in the end results – very visibly in the case of the beans, and noticeably in the improved taste and productivity of the tomatoes. We only have one polytunnel for the tomatoes in 2016, but we got almost as much yield this year from this one than from two polytunnels of tomatoes [ref]We have three polytunnels, all of the same size and colocated[/ref] in 2015.

I know of no way of quantitatively analysing taste, but several of our CSA members observed the much better flavour of our tomatoes compared with shop bought ones. However, one other thing we changed across the years was have a dedicated CSA member Ann look after the tomatoes, pinching out all the offshoots and training the stems along the frames. Because we could not afford a control plot with the tomatoes, the almost doubling of yield could be the result of her extra care and attention to detail, or a combination of the her work assisted by the compost extract.

The compost extract was used in the polytunnel with the tomatoes in July 2015 and some of what was left over was also used in polytunnel 1 which was where the beans were planted, with the ribbon tied to the frame to show the extent of the coverage, the left behind compost after extraction also went into the tomatoes in polytunnel 2.

The beans at the back show very noticeably more vigorous growth and had a much higher yield, and this coincided exactly with a ribbon showing the limit of the compost extract.

Not every attempt showed success – last year we tried some outdoor tests on defined plots in the sweetcorn crop. This crop was lost to the initially wet and dull start to 2015 and not enough manpower for weeding. I felt there was some difference in one of the plots, but not enough to make a clear picture and not enough to redeem the crop.

Continue reading “What I learned over a year of growing with Soil Biology”

Compost from start to thermal equilibrium

a compost heap tracked all the way from start to thermal equilibrium. The sensr for the green trace was reallocated to ambient about 1/4 way through

I recently tracked a compost heap from start to reaching thermal equilibrium. Partway through we started another one, and one of the sensors was allocated to tracking ambient. While a single data point isn’t conclusive, it was interesting to see the week 37 (12-18 Sept 2016) second breath of this heap after the second turn coincided with a week of particularly warm weather. This points to a potential ambient sensitivity and it being worth tracking ambient in future and perhaps insulating the heap more in the later stages.

I will keep the technology of remote temperature sensing here, because I’d imagine horticulturalists aren’t that into electronics 😉