Electronics

Apparently one of the local bike thieves was eyeing up the bike. Certainly a car was driving down the road, crawling opposite the bike, and then driving off again. Having had one bike nicked I didn’t much fancy losing another. Thus we had to make the house look a lot more secure in a hurry; and the shops were closing that evening and not reopening till Tuesday. For it was the New Year.

Every project is a prototype, which calls out for a second version avoiding the mistakes of the former. The trick is to give the prototypes away; then one has a legitimate excuse to make another—and one gains an (undeserved) reputation for generosity to boot. After the quick sunrise alarm clock various things happened, including a ’two week lockdown’ to build up capacity in the NHS, which turned into three months. Thus I was stuck in one part of London, and my fiancée in another, and the streets were patrolled by Dobermans with £10,000 fine notices stuck to their teeth. How to get from one side of London to the other?

This was a sudden impulse last summer: I’d seen a ‘sunrise’ alarm clock (which fades on slowly to simulate sunrise, theoretically bringing you out of deep sleep naturally and waking you up gently). My sister mentioned having difficulty getting up and needing multiple alarm clocks. Ergo.

First thought: where to get the light? I had a look in the LED parts draw, but it was disappointing, as was the draw of old led torches and bike lights. None of them gave a reasonable light: more like a little pin-prick than the sun. So off down the road to the bricolage shop (or bric-a-brack as we call them) and I came back with this:

Dad rather liked my clock. In fact, he went looking for ‘a clock with hands and an adjustable chime’. Which, of course, made me wonder whether I could make one.

The first question was the hands: I liked the leds at the front of mine, and didn’t see the point in moving real hands around with a stepper motor or something of the kind. A digital clock should, I think, look digital. Looking online for things like ’led ring clocks’ showed the odd design, but none with all three hands in one ring, and three rings struck me as a bit much. Thus I started looking on farnell for bicolour leds to make the hands out of, and found an orange/red led on clearance at around 10p each: and also some red/green rectangular leds. Now, wouldn’t it be nice to have the ’ticks’ in the display differently shaped as well as coloured?

I don’t much like PCBs, but I like wiring ICs up even less. Up till now I’ve made boards with the toner-transfer-and-any-old-container method. The trouble is that I hate making up ferric cholride and always make the bare minimum, and during etching the concentration falls off, the rate slows, and you get poor definition and damage. So I decided to make a proper vertical etching tank, big enough to do a large board and still not run out of etchant. Casting about the shed found a large transparent dust-sheet, and I wondered about using it for the tank. With care an unpierced section could be found, and a bag was taped together:

This project began when the noise of the ethernet switch opposite my college room became unbearable. I picked the room for the view, which was sublime: the valley falls away so steeply you can see right down, over the trees, to the river, and climbs again the far side in a steeply wooded bank over which the pigeons perform what I can only describe as buzzing runs on the squirells. In the distance, the rolling hills, at night the moon and by day the sun—morning and evening, opposite corners of the window. Sometimes the outside world would come a little closer:

The radio we use in the kitchen to make washing up bearable stopped working. Specifically, it wouldn’t turn on, but the power LED was constantly flashing on and then fading off. What makes me think the power supply might have died? Lo and behold, after purchasing a cheap multimeter (it’s incredible how cheaply one can get some things now: in ten years the price of test equipment has plumetted): the ‘8v’ output was about 3v, and the ‘15v’ output was 0v. Hmm. Here’s the very crude power supply:

I’ve always thought of those clap-activated switches as a bit of a gimmick—after all, you can always just move the lightswitch if it’s that hard to get at. But currently my mother is hobbling around on crutches, and it suddenly struck me that turning the uplighter on from the doorway would be handy. A rummage through the junkbox found a board—I think from an old washing machine—full of relays, and 5v relays at that, so no need for a voltage multiplier to turn the relay on. I also found an old ‘usb charger’ rated at 1A 4.2V (?!), which is thankfully enough to turn on the relay.

The internet in Durham, which was allowing me to use the workstation there remotely, has gone down; support tell me to ’turn it off and on again’. But obviously I can’t do that remotely. Ah well, it wasn’t really needed. But what if it were? I’ve run servers over unreliable wifi links with good uptime before, with a failsafe script which rebooted everything if it couldn’t ping the gateway for too long—and looking at the logs, sometimes it was needed. But I can’t reboot the router (and though I’ll replace it, there’s little opensource DSL firmware, so I’m never going to be able to reboot the modem). So what we need is the remote equivalent of pulling the plug out and putting it back in again. I have a few of those Poor Man’s Rasberry Pi boards lying around; one could surely be made to pulse a relay if it can’t ping after a while? But the only relays I have (mainly rescued from a faulty boiler) are designed for industrial 24v DC. I hunted for a while and then gave up on finding any 12v relays. Isn’t there a circuit called a voltage doubler? As usual, SM0VPO has some information. I was going to use a 555 timer, but that shamed me: I can still build a discrete multivibrator—it was one of the first circuits I ever built, after all. But first off the relay inline in an extension cord. Here I made a completely daft error: the box is about 100% too long, because I thought the cable exit grommets went the other way round. But anyhow, here is how to make a box out of hardboard, that most intractable thing:

I started this peice of test equipment when I was about 15, I think, built the timebase with enthusiasm, the counting chain with a bit less, and then wondered how on earth I was to attach the 7-segment displays. Surely not one wire each?! So the project languished, and eventually got relegated to the shelf without ever being finished. All I had was the breadboard and two schematics which nearly corresponded with what was in front of me: