Heath Robinson-esque Mechanical Clocks – “COMPUTIM”

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I have half heartily collected clocks for a while now, there is something about a device that measures the passage of time in such a ruthless manor that is somehow appealing. Mind you, I half heartily collect quite a lot of things, its the best way really – no so far into an obsession that people start to talk but enough that you can call it a collection… I generally class it as hoarding but none the less I am quite pleased with this little find. This is a COMPUTIM “digital” clock. It is an electro-mechanical display device (always a good mix). I picked it up for £1 at the boot-sale last week.

COMPUTIM Clock

First impressions would dictate that this clock, baring in mind that it has a C size battery in it, is electronic with a pulse coil to increment the time. When one notices, however, that it is ticking then you have to ask yourself why. Clock clearly should tick, but not if they are digital and have no seconds indicator, and take a battery.

Popping the top and stripping it all down for cleaning revealed the answers. This clock features a full escapement based mechanical clock which ticks away in its own little world. As it ticks, a magnet is gradually brought closer to a reed switch. Eventually this switch triggers and activates a motor which winds the magnet back, winds up the clock a bit and increments the seconds. There is a small adjustment for moving the reed switch so the magnet trips it after 60 seconds.

COMPUTIM Inside

 

Hence the battery is used briefly every 60 seconds to give things a little kick. Genius. This also has the remarkable side effect of this clock making a nice quiet tick and, every minute, a loud and satisfying ”ker-chunk” sound. By sticking this on my computer monitor one quickly becomes aware at how much time you can waste on the internet.

COMPUTIM Inside 2

 

Bargain!

Car Radio Repair – BMW Business / Becker C53

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In 2001 BMW decided to move from Philips to Becker to supply their radios for the 5-series BMWs. My 2001 530 had a Becker c53 Business radio in it which is a cassette radio with a CD changer in the boot. The new Becker radios have flat pins and a strange “Quad Lock” connector on the back. These radios have a design floor in that the power amplifier ICs overheat and die, loosing you audio in one or more speakers. For reasons known only to Becker, they decided to make the power amp ICs Chip-on-Board – black blobs of stuff bonded to the PCB. This gives them shit heat dissipation and hence after a good bit of antisocial music they often shuffle.

The radios aesthetics make it blends into the dashboard in a way that reassures you that any attempt to replace it with a DIN radio will look shit. It also listens on the BMW i-bus and makes use of the steering wheel controls which is an expensive operation to get working on an aftermarket radio. Hence the options to fix this is to either:

  • Buy another C53 radio on eBay  with the prospect that it may also be teetering on the edge of death. This is not an option as they fetch ~£100 or so, which for a radio cassette is just silly.
  • Get a fascia adapter, wiring loom adapter, i-bus audio-leads protocol converter to get the steering wheel buttons going. Looks tacky and works out expensive…
  • Hack another power amp IC into it.

I went with option 3. This is nice as the power amp IC is the last thing in the audio path on Car Radios, the 8 speaker connections on the back (4 channels) go straight to the power amp, along with battery 12v, 4 pre-amp audio signals and a few grounds and standby signals. Lets get hacking. There is a man on eBay who will do this for you for a tidy £100 but if you have an old and tired aftermarket radio like a sony xplod minidisk head unit or a alpine unit with “cd player foobar” written on it then the donor power amp chip is free and the only cost is your time…

Radio pic from google images. You remove it from the car by pulling off the volume knob and using a flat bladed screwdriver in the little hole to rotate a cam that releases some clips :

c53 Radio

 

Once you take the cover off and remove the PCB (don’t forget the metal clip that tries to push the chips back plate down onto the metal casing for some heat dissipation) you will find the power amp ICs in the rear right corner:

Power Amp ICs before amputation

 

 

If you have a desoldering station, you can make some more room for yourself:

C53 radio desoldered

You will notice that all the fat traces go into the connector board, 8 of them are speaker outputs (buzz them out) and there is 2 grounds and 1 battery 12v feeds per chip (iirc – I did this about 2 months ago and am writing this from memory) The 3 SMD components above and between the chips is a thermistor voltage divider to allow the radio to throttle back on power amp overheat.. Yeah, good one. The radio doesn’t seem to mind this being missing, which is good since as the chips are out on a limb, I decided to amputate:

C53 amputated

 

This was then cleaned up and, because tacking the wires onto the PCB tracks doesn’t work in reality, I decided to bind wires on the through hole connections straight on the back of the Quad Lock connector. This radio is quite poorly built in my opinion. Its PCB delaminates quickly and, if you look at it long enough you will notice some very interesting “auto-router-esque” style traces. Designed quickly I would say.

Progression!

The colourful wires are the new wires for the daughter board power amp to connect to and the grey ones are temp wires running to some bookshelf speakers as I didn’t have a handy quad-lock connector to test with. BTW, these radios power up and run fine with just 12v and ground, no need to sense an i-bus link etc. The power amp IC I am using came from a sony xPlod radio and is marked TA8268A, a custom variant on the Toshiba TA8266H chip for which a datasheet is available. They are all much the same, this one is about 4x40W. They have 8 speaker connectors, 4 power grounds, 2 power VCCs, Mute and Standby TTL inputs, Signal Grounds and 4 signal inputs. Also, because the old power amp chips were capacitively coupled we can do away with the signal input caps and tack off the old ones. Simples.

TA8266H Test CCT from datasheet:

TA8266H

 

This stolen schematic shows the TDA7386 wired up and is a more involved example. (TDA chips are a popular power amp which I was originally using for this but killed in a foolish move involving a signal ground masquerading as a 12v line)

Audio Amp 4 channel computer schematic

Get your point-point wiring hat on and get to work. The metal bar seen in the pics above is a convenient signal ground and the 4 large ceramic SMD caps are the signal caps (you can see the brown,orange,blue and aqua wires coming from them in my pic above.

Done Deal:

Done

The big caps are decoupling and reservoir caps on the various power rails. The only complication came in getting a standby signal. This is very important as the chips are fed direct battery voltage, not ignition voltage. Very direct and very hefty 12v. Unless you like jump starting, get your standby line sorted! The original chips seem to have a couple of signal lines which didn’t behave in any useful way in regard to standby signals. I may of killed something by this point but in the end I tacked the TA chips standby line to the electric antenna output driving FETs gate as this had the appropriate logic levels and worked well in regard to de-popping (pre-amp signals stable before firing up power amp).

Reassemble and test. Do not underestimate how hot the power amp chips get! The heat sink pictures above is arguably not big enough! It survives my hour long commute with pendulum at antisocial levels though so that’s good enough for me!

C53 Radio Pinouts

C53 Quadlock Radio Pinout

Happy Hacking!

Electronicon Automatic Lead Acid 12V Battery Charger

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A while ago I had a large stack of battery chargers that came to me via a surplus route, the sort of thing one uses to charge up a wheelchair, patient life, crow scarer or bazooka etc.

These chargers give out 12v at 5A but do so in a somewhat strange pulsed way. They appeared to measure the battery voltage between pulses and move from a “charging” to a “Nearly Done” state at a particular threshold and then go to a “Charge Complete” top-off as some point in the future after that. They seemed to work well enough and I sold many dozens of them on eBay over the years, fitting them with crocodile clips and the like. I had a couple that seemed to misbehave and in a exercise of sheer masochistic tendencies I decided to draw out the schematic. The damn thing was a sheer monolith of analog electronic magic and witchcraft. It required the use of the dreaded OrCAD (my now least favorite EEE package) to sketch it all out.

I do not recommend implementing this schematic, but if you own an Electronicon charger it may help you out at some point.

electronicon_thumb

ELECTRONICON BATTERY CHARGER

This reveals a rather insane mind of design but it is rather clever in some ways. A somewhat overuse of thyristors and a strange 76 minute time delay between “Nearly Done” and “Done” kind of kills the mystery but still…

Take it or leave it…

Steampunk RF receiver…

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This has lived on my desk for a while now, there is actually a sister one (version 2 in fact) that I also created in a similar style – that lives on a different desk though so for another day. This thing is a lovely mahogany box, bakelite top, brass edging and beautiful 70′s indicator lamps. The thing in the middle is a 1kHz beeper (if a beeper can sound polite, this one does). The aerial connects to a fairly modern Scantronic 4612 2 channel long range RF receiver. The rest is pretty much self evident, each channel lights a lamp and beeps the buzzer. The switch allows you to make the buzzer only buzz on one channel or both (3 position). That switch is a 1950′s “Keyswitch” – It is about 4″ long inside. Also in the box is a transformer and rectifier and associated junk to make it run.

Pandora would be proud

The signals to trigger this come from 4 things

  • Doorbell (this is a pull string so a magnet is glued to the string and a reed switch lives nearby.
  • Post Box (This is so overly complex it deserves a website of its own, rest assured light gates, fancy mahogany boxes and lamps / buzzers are involved elsewhere for that)
  • Security beam across the main workshop
  • Pressure mat in my electronics workshop

Hence it lets you know if the world needs your attention when you are in a mind of your own… Funky bit of kit really. Shame it is never switched on :-/

MEM Star Delta Starter Timer Schematic

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If you ever have the joy of tinkering with a MEM Star/Delta starter (automatic job with a timer, 3 contactors and some excessively mind fuckery relay logic) then take note of this: The timer unit runs from a secondary coil wrapped around the STAR contactor coil – it is not mains and applying mains will cause it to suffer. You will also suffer as you will need to fix it. To this end, have a schematic:

Schematic

Note the cheeky thyristor in there to fire the relay coil. You can test the thing from 24VAC as that seems to be what the coil based transformer gives out, though it sags with load quite a bit. The coil was not giving the timer any voltage on my unit so it received a 9 VAC center tapped (so 18vac) transformer from a clock radio instead. Works like a champ now :-)

Here is an RS pic of the unit itself:

MEM Star Delta Starter