electronics – Page 7 – Richard Mudhar

a Raspberry Pi camera after a season outdoors in the British weather

The old pig camera is due for a rebuild. I went with the Pice outdoor case for the new one, but it’s interesting to see how the old one stood up to the weather. It was still operating when I decommissioned it because I needed to scavenge some of the network parts for the new one. In particular I now use a central WiFi/Mobile node to cover the whole farm, and use Wifi to upload the pictures for each camera via that node.

The original one ran the Mifi node and the Pi all the time, which was hard on battery power. Hence the rebuild, but if the case held up over a season I may as well use it rather than splash out for a new Pice…. The original case was larger than it needed to be, but I can now use this space to put the light sensor and 12V to 5V DC-DC converter inside it.

So how did it stand up to the ravages of the elements. When it was new it looked like this

and the innards looked like this

the Pi gets big fast when you hang enough onto it to make it useful

So from the outside it now looks like this

Raspberry Pi camera after a year in the open — Raspberry Pi camera after a season in the open. The messy carving of the rain-shield started out that way

Which isn’t bad. It vindicates one of the things i did, which was to use plastic screws for mounting. Unfortunately the camera needed M2 screws which were steel, and these rusted. The sun bleached the tape, but the box itself stood up to the light well.

The cheap Chinese DIN socket is starting to rust

I had fitted this on the underneath of the case. There are two philosophies when it comes to trying to run electronics outside. One is to go IP65 all the way and keep water out, which means waterproof enclosures, Dri-Plugs for power etc – you’re looking at about £20 to get the power through the case and maybe another £20 for the case itself. Farm hacks don’t really need that sort of ruggedness, which brings me ot the other philosophy

Accept water is going to get in. Mount all connectors on the bottom so it can drain out. I actually picked this up from the PICE guys – they mount the raspberry Pi on the lid of the case, so water could be standing on the bottom half and it would be okay.

No evidence of water, no creepy-crawlies - great — No evidence of water, no creepy-crawlies – great

As it was no water seems to have penetrated, no creepy-crawlies seem to have got in. The latter are a pain with electronics outside- they seem to be attracted to the heat, or maybe the power itself. It certainly helps to lift the device into the air, or simply put it on a stick a metre or so high, compared with ground mounting. But this looks clean, there’s a little bit of evidence ingress on the seam, and the PVC tape degraded in the UV so this may be worth some thought. I will re-use this box, mounting the microcontroller timer and the light sensor on a board set into the rails, so I don’t have to drill the box for mounting.

However, one thing has been impaired, and that is the lens of the camera, which gives a hazy effect – it was clear and not foggy when this picture was taken

Flare on the camera lens after a year in the open — Flare on the camera lens after a season in the open

Normally a CCTV camera is behind a piece of glass to keep the elements out and now i know why. Cleaning the lens with IPA didn’t help. I am tempted to glue a piece of microscope coverslide over the tiny lens in future this would have the optical quality and would be cleanable/replaceable. Continue reading “a Raspberry Pi camera after a season outdoors in the British weather”

Fixing a Maplin EAP450 Car amplifier

This amplifier is used for parties at The Oak Tree where we have no power on site – a 12V leisure battery is good for about 7 hours. I’d noticed one of the pots getting scratchy so one of the four channels was low. This is a four-channel amplifier, and I use it bridged 2×2 as my speakers are 8 ohm. The amp works but I’m losing power, experience tells me this sort of fault doesn’t fix itself.

The go-to site for car audio tech is Basic Car Audio Electronics so if you’ve blown your amplifier and are looking to fix it then that’s a good place to start. The tl;dr version is it’s probably not worth your while, get a new one. The trouble with blowing the amp is not only do you have to find and change the blown part, but also establish the rest of the parts are okay. I’m just fixing a passive part in an otherwise normally functioning amplifier. It’s probably still not worth my time but it’s criminal to junk the amp for the sake of £2 worth of parts.

I did get a meter on one section of the pot and established that it is intermittent and ratty. So I didn’t need the schematic. It’s nice to have, though, but knowing Maplin I figure it’s probably not worth calling them up and asking them to send a PDF or a dead-tree version through the post. I’m still sore about the way they washed their hands of a portable TV that failed after 15 months. On investigation it has clearly not worked right and been incompetently hand-repaired at the factory leading to the screen failure.

Inspection of the circuit board and a bit of Googling turns up some leads. I observe the circuit board is marked APA-450 Rev 2 and Googling APA-450 tells me that Clarion used to make one of these, and the control panel looks suspiciously similar. So now I know what a Maplin EAP450 is – presumably they bought the rights to rebadge this discontinued Clarion amp in a different housing. Or perhaps there’s some noname Chinese company in Shenzhen hawking their production line to whoever will pay 🙂

I got the service manual and schematic from those nice guys at Elektrotanya and established that the part numbers tally with the board.

plan A – changing the pot

Ebay was my friend in sourcing the pot, as it happens also from China. One of the great things about Ebay is the variety – it’s important to get the length of the splined shaft right so it doesn’t stick out too far and this is a slightly oddball length. A 6mm spline shaft is close enough.

Pots showing diferent pitch — Pots showing different pitch

I got that right, but I was caught out by the pitch of the pins being smaller than normal. I’d already dismantled the amp before I spotted that. D’oh.

Take a photo before you dismantle the amp

You can’t have too many decent photos of the gear before you take it apart . Once I had taken out the screws I got to see the PCB – it’s clearly not the finest reflow job I’ve ever seen

plan B – fix the original pot

Time for Plan B – dismantle the offending wafer of the pot.

By carefully bending the tabs I could get the wafer out and look for the problem – there’s a faint patch of shiny something not right at the top left of this, which I cleaned off with some isopropyl alcohol. Plan C was going to be replace this pot and the other one with two fixed resistors per wafer. There’s no real need for this sort of control on a power amp. Ideally I want to line the amp up for full-scale output at +4dBu – there’s far too much gain and it needs pulling well back. the line level input sensitivity is specified as 200mV to 6V

final test – success

This is the amplifier at just over 40V p-p showing the two bridge amplifier outputs which are out of phase (I am too cheap to get the probes to set the read out right, so it shows 1/10 of the real sensitivity)

and the final trace shows both bridged sides going into clipping at the same time.

Bird recording in the field with a GPS and audio recorder

After a long break, I looked at getting back to using Birdtrack. When I used it before, I used an audio recorder and a GPS, taking a waypoint with the GPS and identifying the bird and waypoint in the audio note. The advantage of this is I could automate taking in the position data, and just transcribe the bird and count.The obvious way to do that now is to use something like the Birdtrack app. Trouble is this wouldn’t run on my device. That wasn’t the main problem, to be honest, it’s easy enough to solve by chasing the upgrade cycle. There’s a deeper problem – it’s not what I want to get out into the field to do, to spend more time peering at an illuminated screen. Not only would Eckhart Tolle disapprove, but you also have to take your eye off the birds. Don’t get me wrong, the BTO have probably done a great job with the app, and if that’s how you want to list birds that’s great, each to their own. It’s just doesn’t do that much for me. But it’s a continuum – after all, what is the real point of recording what you see anyway, particularly as I’m not particularly good with ID so have to pass on a lot? easygps

Surveying an area repeatedly does mean I get to build up a spatial map of territories and get to know some of the birds by the foibles of their song. Now this is made easier I will see if a picture of territories does build up over time in the breeding season. GPS audio mapping isn’t a new idea, I came across it from the OpenMap community, who had largely solved this problem with audio mapping. They simply leave the recorder on capturing a stream of consciousness, because they want to capture data about the whole environment, that’s what a map is. It makes the synchornisation problem easier, as they set a datum at the start of the run, doing the same job as the clapperboard in shooting a movie. The GPS track is a log of where you go, with the sections individually timestamped, which I hadn’t realised. So start the recording at a datum point, and you know that the audio runs in sychronism with the GPS. Modern digital field recorders are crystal controlled to about 100ppm – about 4 seconds off in 10 hours.Now I don’t really want to spend as much time writing up a trip as doing it, so I took a leaf from their book and used a Perl script to parse the GPX data tracklog, find the nearest section to the audio clip timestamp and create a waypoint there, with a link to the audio file in the same directory. Rather than making one massive recording, I can simply make short audio notes when I see the bird, and the Perl script will tally the record time and sort out where I am. It’s easier to find a record and there is much less audio data to process.

Due to the vagaries of real-life devices you have to be able to put in an offset to take out summertime and any slight differences, but an error of 1 minute at walking speed isn’t so bad for bird logging. At a steady 3mph it’s about 80m uncertainty, but in practice you tend to slow down when observing birds, improving the accuracy. File timestamps do go down to the second, but keeping the clocks within a minute is a big ask. The GPS timestamp is always very accurate because it is set to an atomic clock, so it’s down to setting the recorder properly. Or identifying the skew properly at the combining stage.

As an added bonus, this can work on my field recordings too, I can just save the GPX file and I know where they were made too. Using something like GPS Visualiser I can see where everything is on a Google map.

For bird logs, I need to open the audio and edit the waypoint names to the BTO two letter short codes of the sightings, comma separated if there are several at one point. A second run through another script expands these into the long names and creates an Excel file suitable for uploading to Birdtrack.

Raspberry Pi Soundcard From Logitech Headset

The Raspberry Pi has no audio input, and I had a pair of Logitech USB headphones that had gone faulty – the earth on the headset was a dis. The USB part seemed to work, but headphones live on borrowed time, connectors and wiring tend to go, and everything is sealed, So I wondered if I could reuse the circuit board as a Pi soundcard. Stereo output but mono on record, of course, but still useful. It’s all part of experimenting to make a low-cost audio field recorder that can start by itself. Nothing is designed to be repairable here, so the plastic USB module case was pinged apart with a flat-bladed screwdriver. Initially I wondered if the black stuff was a blown capacitor, but it was on both sides of the board so I figured it was probably glue from the connector, which was confirmed when I unsoldered the connectors, it came off like a gluey film.

Logitech A-0365A USB headphones control board

Headphone cable uses fine strands of individually enamel insulated wires wrapped around a synthetic fibre core. The good thing about this is your headphone cable breaks later than if you used normal multi-strand audio cable, given all the flexing it has to take. The bad thing about it is it’s the devil’s own job to solder, because as you heat the strand the synthetic coating melts, robbing you of heat and re-insulating the enamel you’ve burned off. So I unsoldered the existing cable and threw it out, and soldered a stereo jack plug for the headphones and a phono line socket for the microphone. I then extracted the original microphone capsule from the headset and soldered it to a phono socket just to test this out in the original circuit conditions. Continue reading “Raspberry Pi Soundcard From Logitech Headset”

Flat Screen UIs make Fumbling Fools of us all

Did the music for a wedding using my PA today. The bride and groom were lovely, friends of ours and at was a great day. A wedding is an odd PA/DJ sort of job, It’s not the same as a party, or even running a mixtape for a party. Most of it can be scheduled up front – to the extent that there are firms that hire out a no-DJ wedding system

The job was made easier for me as the bride had made her selection of classical music, with a section for the getting seated bit and a long stretch for the after the event part. So far so good. The venue was the lovely Christchurch Mansion in the main park in Ipswich, and the weather smiled on the happy couple for the event and afterwards

So all I have to do is run the playlist. Because this is classical music the sequences are long, and you don’t have to do the DJ crossfading thing between tracks. Easy-Peasy, right?

Wrong

Some parts of a wedding are a stage show. Stuff needs to happen in time. Usually there’s the entrance of the Bride, and the signing of the register. Both of these are a performance, and timing is crucial. Whatever you do as the music operator you do not want to screw this up the entrance of of bride, in short you need to know that your music is gonna start on time, every time, and you are going to fade it out at the right point. The bride selected Pachelbel for this

The registrar also has to say various things at various points, and they don’t want the music to be running while they’re talking. With classical, pulling the music is easy as a fade down – it’s a bit more of a drag if you have to fade a pop song just as they are getting into the main part, you probably have to rehearse timings, but this wasn’t a problem I had.

Making the right thing happen, on time, on cue is not easy with an i-anythingwithatouchscreen.. It might be easier with a Nano or something with an old-skool gonzo keypad and LCD, but a touchscreen is a vile UI for this job. Not only is there a little bit too much latency between the press on the screen and something happening, but it’s far too easy to screw up and then you have to pad your way through a series of menu choices to say no that isn’t what you want, you want this to happen instead. Continue reading “Flat Screen UIs make Fumbling Fools of us all”

Adapting A Makita Universal Charger For Other Nimh Batteries

We standardised on 18V Makita NiMH cordless drills at the farm. NiMH is older tech and heavier than LiIon, but the price/performance seemed to be about right there. We’re not hauling these up ladders or carrying them for miles. The trouble with cordless drills, well the NiMH ones, is that you have to stop using the drill as the battery runs down – when you hear the change in note as the power fades, switch the battery. If it’s you who will be paying for the replacement battery you will do that, but if it’s something used by many people that doesn’t happen, because it’s hassle to go get another battery.

Under the harsh load of a drill, that means as the voltage of a cell falls to 0, soon current gets forced backwards through the weakest cell and it dies. So you get a pack with a few duff cells in them, and have to junk the whole thing. The moral of the story is change the battery as soon as the sound changes and the power drops…

Continue reading “Adapting A Makita Universal Charger For Other Nimh Batteries”

setting the time on a cheap bike DVR

This DVR is a fine ebay noname special, and the way to set the time is to create a file tag.txt with the following format

[date] 
2014/07/27 
15:43:24

Continue reading “setting the time on a cheap bike DVR”

PICE case and WiFi upgrade for the remote farm camera

The issues with the Raspberry Pi farm camera were of waterproofing and of iffy Wi-Fi range. Both of these are addressed in the new version. The PICE waterproof case from the guys at EdVenture marshals this motley collection of bits

into something a bit more organised. There’s no getting away from it, the PICE is quite expensive at about the same as the Pi itself, but it does solve a lot of the mechanical problems of trying to run a Pi outside with a camera. The landscape version is the one i needed, since the case is only water-resistant with the top horizontal – the Pi is mounted on that and even if water does get in it falls to the bottom away from the Pi. The previous version of the PICE took the picture in portrait mode with the case oriented for best water resistance, which isn’t so useful for our aims.

This is a good interim solution – it gets the cameras into a tighter configuration, and should let me pull back the main MiFi box back to a more central location to serve the rest of the cameras. As a result each camera will draw less power which is good. The Edimax EW7711 USB WiFi unit has a better performance than the USB nano-dongle – the reason is obvious when you look at the size of the aerial of the nano

size really does matter in some applications, and and aerial much less than 1/4 wavelength is going to struggle to get the signal out

although it’s 2.4GHz the wavelength is still 13cm; you still need to get enough metal in the sky to get the 300m path length to work, unless you can mesh. Continue reading “PICE case and WiFi upgrade for the remote farm camera”

Remanufacturing a 12V power tool battery

Cordless power tools often die not because they’re worn out but because the battery fails, or only holds a charge for a short time. Every tool’s battery pack seems to be different, either from the sheer cussedness of consumerism making you buy a new tool, or because nobody has standardised battery packs, You can fight back, because though the battery packs are all sorts of sizes, the parts inside are usually drawn from standard sized parts, they’re merely packed in different ways.

I had a cordless strimmer, once advertised years ago in the Guardian, from a no-name supplier with two battery packs. Both of which are now duff – a strimmer is a fairly hard life for the battery packs with about 50-100W. Here’s how I remanufactured the battery packs. These are NiCd battery packs – the key issue to to replace like with like. You can replace NiCd with NiMh but don’t cross any other chemistries.

Continue reading “Remanufacturing a 12V power tool battery”

Remote Farm camera – experimenting with WiFi

Clive from the Raspberry Pi Foundation very kindly let us have a Pi Model A and camera, so it’s time to take this project forward a stage. At the moment the alpha test version is in service keeping an eye on our new piglets. Although the original purpose was to keep an eye on our newly arrived cattle pigs are more enterprising, so it’s good to know where they are

Development was stalled however since it’s not easy to work on a piece of kit in service. Ideally one MiFi box could serve a number of cameras. This would reduce the camera power drain and consolidate.

The trouble is that the site is on the edge of town, a couple of hundred metres from the nearest houses, and I want to use BT Wi-Fi

I acquired one of these from ebay I didn’t have much hope for the integrity of the device, and to gain height I needed to go 250m further way from any likely source of WiFi. But it worked a treat, as a WISP client, I’m amazed. I was able to see 18 access points, five of which were BT WiFi , 3 of which were 5dB or above. The TP-Link gives a decent link at more than 5 and nothing at 2. I streamed a video to confirm the stability of the link.

I use it with a TP-Link TL-WA5110G which has the advantage of having a sma antenna socket and a native power supply of 12V. Although the adaptor is specced at 1A I measured the power drain at about 210 mA (~2.5W @12V). Which isn’t great but not terrible

A WISP client is not a repeater

The trouble with using the tP link as a WISP client is the signal is presented as Ethernet, and I’d then want to re-radiate the signal on a different Wi-Fi network. I could set it as a repeater, but then every Raspberry Pi would have the hurt of logging into BT WiFi. Whereas if I use a Raspberry Pi connected via ethernet to the TP-link and a WiPi dongle to connect to the farm I can collect pictures from the cameras on the farm network and perhaps power-manage the TP Link to only update every so often.

So an unexpected win, and I can look at using a Model B as a concentrator