RSPB Ipswich Local Group leader Chris Courtney and a group of our surveyors met up today at the Brunswick Road Recreation ground for a press event to celebrate the completion of the survey in 2016. (above pic is Chris (L) with Joe Underwood, Ipswich Parks and Wildlife ranger)
Chris Courtney, Ipswich RSPB Local Group leader, and Joe Underwood, Ipswich Parks rangerHeatmap showing the density of sparrows in Ipswich
Naturally if you’re in the group being photographed you don’t get to take pics of the group 😉 It was good to meet up and put some names ot the faces of our sparrow surveyors from last year and talk with the rangers, who have improved this rec for wildlife.
Alanna, intrepid surveyor of seven Ipswich squares in 2016. Behind is the part of the rec that has been made more wildlife friendly by the rangers and another sparrow colony has been established.
There’s something charming about the few pedestrian level crossings that take footpaths over the railway, reminders that the footpaths were here before the railways.
In an attempt to show how lethal these things are, or perhaps how much the pedestrians are in need of a Darwin award they have erected this panjandrum to bark out dire audio warnings about walking into the path of an oncoming train while you are glued to your phone, distracted by children and various other hazards.
Fonnereau way (Westerfield) pedestrian level crossing
I stood by the annunicator tripping the PIR sensor to get the full sequence of announcements this thing barks out at passers-by. (recording edited slightly to shorten dead space)
To be honest, if you don’t pick up that something is amiss when you see this
and hear this
then you’re tired of living and should spend all of your time in your phone, else go collect your Darwin award.
Network Rail is trying to harangue the local landowners into going along with their scheming
flyers posted by Network Rail’s henchmen
The Fonnereau Way has been used for a long time, although it’s been the subject of a fight when someone into horseyculture bought a property in 2009 at the Westerfield terminal, claiming to be all surprised there was a footpath there, trying to block it up and have it stopped on several occasions. Unsuccessfully, it appears. Nevertheless, Network Rail may yet succeed.
The British Museum in London is full of all sorts of oddball items. Some of the things on the ground floor are much more in the line of the cabinet of curiosities than the themed collections upstairs. As you turn to the left after coming through the main entrance there is a Victorian room dedicated to the Enlightenment. Although the cabinet of curiosities approach is frowned on nowadays, it appeals to the randomly curious part of me. It’s home to a small collection of John Dee’s magical items
Here we have John Dee’s obsidian scrying mirror. Obsdian is apparently a natural volcanic glass formed from solidified lava, and can be polished to a smooth dark surface. I didn’t notice from the description, but apparently this comes from Mexico via the Spanish.
John Dee’s obsidian scrying mirror
It’s the devil’s own job to get a picture of this in the dim light of the Museum, and taking a picture of a black object is never tremendous fun. John Dee entered Cambridge university at 15 and graduated two years later. He taught at various European universities before returning to England when he was 24 to teach navigation and mathematics to captains of the British Navy, playing a key role in the fight against the Spanish Navy.
Astronomy and astrology were linked disciplines at the time. Dee was imprisoned in 1553, allegedly for casting a horoscope for Elizabeth, Queen Mary’s sister and heiress to the throne. It’s easy to see how he got into hot water – the horoscope indicated Mary would die, and Dee was charged with attempting to kill Queen Mary with sorcery. He was released in 1555. Elizabeth became queen in 1558, and Dee’s fate improved.
Instead of scrivening mirrors we have computers and they operate not on unseen angels but on unseen electrons. Because of his failures Dee remains modernity’s dark and forgotten twin. We are able to live in a world that he could conceive of, but one which he could have never invented.
Dee is best known now for his work on occult phenomena and contact with the spirit world, which he began in earnest in 1581. He found this contact hard, so he starting doing this work third-hand, by employing gifted ‘scryers’ – people who could see the spirit world directly. Using scryers enabled Dee to take comprehensive notes. He first worked with one individual, Barnabas Saul, until Saul was burned out from some disturbing encounters, and Dee searched for a replacement to help him.
In 1582 he found him, in the form of the imperfect rascal Edward Kelley. Kelley was a sensitive, but also a charlatan, whose ears had been cropped for forgery, so he was difficult to use as a witness. Dee’s notes indicate that in November their spiritual research encountered the Angel Uriel, who instructed them to create a talisman that would make communication with the spirit world easier. Dee and Kelley constructed these and other magickal tools.
John Dee’s wax tablet with Enochian script
This breakthrough led to Dee using a novel language called Enochian script, and the pair made significant progress, and their fame spread. This led to sponsorship from a Polish noble, who was dazzled by Kelley’s scrying ability when he came to England, and who funded the pair’s attempts to discover how to transmute iron into gold. When the noble’s money ran out, Dee and Kelly were sent to Prague with a letter of introduction to Emperor Rudolph II. This began auspiciously, as Rudolph was also attracted to the possibility of the Philosopher’s Stone, but naturally their experiments always remained on the verge of success without actually delivering.
Dee’s reputation as a wizard caused problems at home in England, where in 1583 a mob attacked his home in Mortlake and destroyed his books and instruments. His fortunes started to decline when the Pope instructed Rudolph to expel Dee and Kelly, and they sought sponsorship for their work from King Stephen of Poland and another noble, Count Rosenberg, who accommodated the pair in his castle.
Kelley’s mischief meant that they parted their ways when he made some unreasonable demands of Dee, who then returned to England in some style in 1589. However, without Kelley he now relied other scryers who were even less reliable than Kelley. Dee held a few more posts before retiring in 1603. Dee died in relative poverty in 1608 – Kelley had perished in 1595 jumping from a window escaping from a Prague penitentiary.
A fascinating diversion into Elizabethan intrigue and mystical inquiry, brought on by a chance visit to the Enlightenment room. A few cabinets down is fellow Cambridge alumnus Stukeley’s romanticised picture of A British Druid in his 1740 book “Stonehenge, A Temple Restor’d to the British Druids”
Picture from William Stukeley’s Stonehenge, A Temple Restor’d to the British Druids
which is why Druids have been associated with Stonehenge ever since. All part fo what makes the British Museum a wonderfully diverse way to pass a couple of hours in London.
The RSPB Ipswich Local Group surveyed the town’s sparrows last year, and we have the results now in. It’s a little bit better than I had thought – strongholds to the north-west and south-east. It’s tough to compare this with the 2006 survey because that wasn’t controlled-effort, although at first glance they still seem to be losing the fight around the Valley Road area relative to the earlier survey.
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’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.
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.
failed 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.
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.
Close-up of 160901 compost
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
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
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.
SR04 ultrasonic ranger module
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.
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.
my Olympus recorders
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
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 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 lowStop 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)” ↩
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?
The polytunnel with the tomatoes
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.
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 😉
