Sunday, 28 February 2010

Car LCD test fit

No wiring yet, just seeing what it looks like.

I figured out why the input part of the Psion board wasn't working, I had the INs and OUTs back-to-front! Hopefully get this fixed on Tuesday and then add the H-Bridge drivers for the motors.

Electric Buggy

The buggy started life as a toy Lamborghini running on 2 6-volt motors, one driving each rear wheel. When we moved house I took the opportunity to ditch the upper body which had seen better days leaving a bucket chassis.

It has 2 6-volt emergency lighting lead-acid batteries wired in parallel to give a whopping 20 Ah. Most of these electric toys have batteries around 6-8 Ah. It doesn't go any faster, but this gives a much extended running time.

These are the new wheels on the buggy up close. I got these hand-truck pneumatic wheels on eBay for £15 and my colleague Johnny kindly helped me adapt them to fit on the buggy. I finally got time to drill holes in the axles for cotter pins to make sure the wheels won't fall off. It's unlikely this would happen because the washers behind them are a very tight fit, but better to be sure where children are concerned.

Friday, 26 February 2010

Arms and The Man

I got a little more work done on the Psion 2 interface board, but I'm getting some spurious results on the input port, so I'll concentrate on finishing the output port tomorrow by adding the 2 H-bridge ICs to drive the Lego motors.

I dug out the robot arm and started testing it. This was built about 5 or 6 years ago, but never used in anger until now. The rubber band belts had dozed so I've replaced those and checked the mechanism for free movement. I need to add pulse and limit switches to it to finish it off.

The arm is holding a Lego satellite dish in it's grab in the photo.

Thursday, 25 February 2010


This is another approach to putting electronics into a car on a very tight budget.

A kind donor gave me a broken car DVD player set with 2 nice 7 inch monitors. A bit of re-wiring and they now have simple 5-pin DIN plugs carrying power, video and audio. I then acquired an old VGA-to-Video adaptor that had lost its leads and power supply, but that was easy to sort out and here we have a test bar graph application running from an old laptop. The program was written in C using the OpenGL graphics libraries and runs under DOS.

I've re-created this in Linux, but DOS has a lot going for it in simple applications like this, most of all the fact it runs in RAM so is ideal if you're using a compact flash card as an alternative hard disk drive. Fewer writes to the card the better.

Wednesday, 24 February 2010

Woof Woof-er

Speakers I got on Freegle and re-built. They were Sanyo mid-price ones which had pretty much burned out. I was kindly given a pair of Bose speakers that were about 25 years old, but the cases were knackered.

So the Bose drivers were removed and transplanted into the Sanyo cases and viola...

The red things are bits of cardboard to cover holes where the original mid-range drivers were, the Bose mids are underneath in new holes I cut out. The cardboard vibrates nicely though creating some sort of baffle effect.

They sound amazing, driven off my genuine 1980s tuner-amp I got for £3 in a charity shop.

Cheap as chips.


After years of trying various compilers for PIC programming I finally stumbled across JAL (Just Another Language) and haven't looked back. Apart from the fact it is an open-source compiler, it's really good and produces pretty tight code. The libraries are superb and the users very helpful to newbies through the JAL Yahoo group.

JAL is similar to Pascal in feel, but so easy to learn that any competent programmer should be able to master it in an evening.

Speaking of which, I may be getting back into web programming, which really stretches the mind if (as I did) you do everything from first principals.

My last project (see above) involved using PHP, HTML, CSS, JavaScript, MySQL and Bulgarian Cabernet, sometimes all at the same time.

PIC Servo driver

Many thanks to Nathan for donating some servos for me to play with, here are the first results...

This is a simple start to driving servos from a PIC using the venerable 16F84. On power up, the PIC resets the servo to the mid position and then waits for one of two input pins to go low. One makes the servo swing to the right and the other to the left. The total range of movement is sub-divided into 100 steps so accuracy is good.

I'd like to use this in a scanning security camera application with some sort of simple motion sensing using maybe ultrasonics.

PIC Vehicle Diagnostics

Old 80s cars with an ECU (engine control unit) don't have the luxury of an ODB interface, but often the signal levels are a neat TTL 0-5 volts from the sensors. Engine speed may be a series of pulses, but a frequency to voltage chip will get a nice voltage for you to measure.

This device uses a KS0108 graphical display driven by a nice I2C interface to display the voltages read by a 16F873 PIC on 4 of its A/D pins. The display is just a horizontal bar with a label for the engine parameter being measured - boost (forced induction engine), oxygen (lambda sensor), engine speed and fuelling level.

The strange item on the right is the steering column stereo control from a scrapped Renault Laguna. This is wired as a 3 x 3 matrix with only 7 switches implemented. Two of these switches, [Vol +] and [Vol -], are used here to cycle up and down through the 4 engine parameters being measured so the driver can change this from the steering column.

Psion 2 Interface

This is my first foray into interfacing to the Psion 2 organiser using the circuits and machine code routines provided on Org2.

So far I just have an 8-bit output port working (using a 74LS374) and to test this I rigged it up to my trusty serial LED display. This display was salvaged from my first ever CD player (bought in Dixon's in 1988) after it finally died. It's based on an M5450 serial LED driver chip and is easy to communicate with over 2 wires (clock and data).

The Psion 2 archive...

Eventually I want to get this working with my 'classic' Lego robotics (4.5 volt motors, very home brew) and finally get the Lego arm working properly.