JDA Design

J M Davis & Associates

Some recent projects

Sunbed Controller Electronics

A couple of drop-in replacement boards for controlling a sunbed; a power board stuffed with dirty great relays and a controller board based round an Atmel microcontroller with a 3-digit numeric display. Lots of timing. (Oh, and the customer wanted a display which just showed nothing but the name of the sunbed. One of those marketing decisions which engineers don't understand. It must have worked, though, because they've sold loads of them.)

PWM vibrator drive

No... not that... this is an industrial application for driving vibratory conveyors at variable amplitude & frequency. Output drive to 6 Amps at 240V, so moderately chunky IGBT's and big heatsinks. The first prototype has four independently controllable outputs, but it's come out a bit big so we may modularise it in the future.

Phase angle control of IR heaters.

IR heater + phase angle controller chip + triac... we also looked at remote control options for this and a cunning scheme for controlling output by the ambient air temperature.

Pill Counter Detector Head.

These have two boards - a line of LED's facing a line of sensors - and control to make sure that at any one time just one LED is on and the output from one sensor is evaluated. Then you need to switch everything quite quickly so that the whole sensor area is swept in less time than it takes for a Sweetex tablet to drop through. Then we needed some automatic gain control so it carried on OK if it got dusty or as the LED's aged, and we stuck on a tiny switch mode psu so it would work off power rails from 8 - 24 volts and never get hot.

Magnetic card read/write board

A drop in replacement for obsolete & unreliable boards in a plastic card encoding machine. The write side is just switches, the read side used a Mag-tek chip for the f2f decoding and a little bit of additional circuitry to detect drop-outs (when there's a fault in the actual magnetic tape and the output drops). Been working well for a couple of years now.

Miniature Industrial Weigh Module

Lots of stuff on a very small PCB. 8 - 24V dc supply, should drive up to 4 * 350 ohm loadcells. Ultra low drift/ low noise front end amplification, big analogue filter ( in our experience nothing beats getting rid of the nasty stuff BEFORE you digitise it), 24 bit delta-sigma adc chip. Big controller chip (Atmel AT90CAN128). RS232, RS485, & CAN interfaces.

LED Lamps

Using high intensity white LED's to illuminate the target for a DataMatrix barcode reader. Our only claim to fame here is sticking a rectifier on board so it can run on 12V ac or dc and can't be wired up backwards. We've done designs for these in quite a few different shapes...

Flickering Quartz Lamps

No really. They wanted three quartz lams to flicker "like a fire". We used some little IR solid-state relays and a micro controller to implement a software version of a pseudo-random shift register thingy. It all ran off the 12V transformer for the halogen lamps and worked surprisingly well, but the project sadly (?) went no further. However that led to...

Envelope thickness detector (2)

The old analogue thickness detector had worked well for years but it needed to be a bit more flexible, so we added some more bits to the flicker circuit board and produced a mark 2 version which automatically detected the highest point in the envelope thickness - where the plastic card was - and triggered on that. We also stuck in a few other bits and bobs to make the board more of a miniature general purpose controller and in due course...

Autoclave cycle complete detection

...used it to detect when the cycle of an Autoclave was finished by monitoring the door interlock solenoid and transmitting the fact to a monitoring PC.

Details of older projects.
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