The Mongrel

What has USB, a Delta-Sigma oversampling DAC, integrated circuits, an old school tube, and MOSFET output drive?

I call it a Mongrel, because it’s got a bit of everything in it.

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Don’t buy garbage

I often hear expectations on what electronics “should” cost being set based on the cheapest price available on Ebay, Aliexpress et al.  Everybody loves a bargain, but the old saying “you get what you pay for” is just as true as ever.  What worries me is that by paying for junk, rather than quality, consumers are voting with their wallets for an inferior technological future.

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Taming the rPi Touchscreen PCB

After my last article‘s mission of discovery I set about trying to stop the rPi Official 7″ Touchscreen from interfering with my 2-way radio.  It looked like the LCD ribbon cable was broadcasting spurs every ~1MHz or so right through the VHF range.  I acquired some adhesive copper tape thinking I could shield the cable to prevent the noise from escaping.

The copper tape arrived, and despite wrapping the LCD ribbon cable and grounding the copper tape it failed to provide any shielding benefit.  Nuts.  So what else can I try?

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Raspberry Pi Car Shield

Raspberry Pi 2 + Power supply PCB + 7″ TFT

I’ve had an aftermarket ECU (Adaptronic) in my car for a little while now, and I wanted some extra dash gauges.  My car (Nissan R34 GTT) has a spot on the dashboard perfect for a 7″ TFT.  Raspberry Pi is the obvious choice, However, you can’t just run a Pi directly off the accessory power in a car.  Aside from voltage conversion, graceful shutdown is also mandatory!

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Raspberry Pi Webcam (Fishcam)

One day I was looking at my fishtank and thought it would be nice to see my fish behaving naturally.  The problem with sitting in front of the tank is they recognise someone is there and go into their “feeding” pattern – rising to the top of the tank in expectation of food.

If I added a webcam, I could push my  RPi temperature display into service.  As a bonus, I could measure the temperature of the tank at the same time.

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RPi SD Card corruption, a new kernel, device trees and a lesson learned

I recently fell victim to the perils of my own laziness.  Rather than gracefully shut down my Raspberry Pi in order to move it, I pulled the power cord.   I had done this dozens of times in the past with no ill-effects but today was my unlucky day.  The Pi did not come back!

Unfortunately, this snowballed from a simple file corruption issue into a full reinstall, which ended up using a different kernel version that broke my custom 1-wire bus setup.  Great.

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Fixing Random Electronics

Last Xmas I bought myself a quadcopter, and have had fun flying it.  Unfortunately after an “attack of dog” (a friend’s dog was trying to be helpful by retrieving the quad any time it landed) one of the motor wires broke.  Rejoining the wire was a snap, but the quad did not turn on.  It just gave a brief flash of its LED before switching off again.

I had a close look at the main board and found a generally shoddy soldering job – look for the upside down resistor!  One of the components was also missing (blacked out in the picture).  So how to identify and replace this mystery component?

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Pinoccio Project #3 – How cool is your Pinoccio?

My freezer has a bad habit of icing up.  It’s not a great design to start with and I suspect I’m overfilling it, but I wanted to check whether it was getting down to the right temperature and also whether the defrosting cycle was running properly.  A Pinoccio is an ideal thing to check this with, the only problem is Lithium batteries don’t like working in cold temperatures.   At -20°C the chemistry inside the battery is finding it really tough going – after a short trip into the freezer my Pinoccio’s battery was reporting 4% even though it was fully charged moments ago.

There is an alternative though, a supercapacitor.  Capacitors don’t particularly care about the cold since they don’t rely on a chemical reaction.  Capacitance is simply an electric charge difference between two conductive plates that are close together.  Supercapacitors with an industrial temperature rating (-40°C to 85°C) are quite common.

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