16 channel output board...

[geneb]

This is a little project to allow you to drive 16 channels of digital output. Each channel can draw up to 500mA at 30V.

The board is 2.1" by 2.85":


The firmware, board files, schematics, etc. can be found here:

http://www.simpits.org/geneb/wp-cont...16_project.zip

I've ordered blank boards today and I'll be selling them (the ones I don't consume myself) for $10 each (most likely). Everything you need to have your own boards made are included in the zip file listed above.

Enjoy!

g.

[Leo Bodnar]

Hi g.
It's a nice little board!
Make sure you read ULN2803A datasheet correctly.
Absolute maximum rated current for all 8 outputs combined should not exceed 2.5A.
It is safer to limit current per output to 300mA unless software/firmware tracks the total current per IC.
Cheers
Leo

[geneb]

Thanks for the tip Leo. I wonder if the full output can be realized if you heatskink the chip? They're only .45c each, so as long as you're using sockets, it's not that expensive to experiment. I've got 74 outputs at 24vdc to run through them - just between the Master Caution panel and the BIT panel in the F-15.

g.

[Leo Bodnar]

I don't think glueing heatsinks will help much. Pins (specifically GND) actually transfer the heat very well so using sockets might be counterproductive.
It is better to use thick PCB traces and fill PCB areas with GND copper and let it help dissipate heat too.

You are right that the heat might be an issue: from the same datasheet the prediction is that at 30 degrees C ambient temperature your IC can dissipate only about 1.6A in total.
Otherwise the silicon will exceed 150C max temperature.

Still 74 outputs with 24Vdc at 0.2A each is 355W. Remember, it's all going end up as heat!
What are you powering??

[geneb]

I'm going to be driving the Master Caution panel and the BIT (Built in Test) panel for my F-15. I think the lamps they use draw between 100 and 150ma each. It's been a while since I looked at the stats. If it comes to it, I can always break it out to another board that uses solid state relays. That's what I'm going to use to drive a motor for the stick shaker I'm working on for the Me-109F/X cockpit.

g.

[Kerbo]

This looks great, thanks for sharing your project.

[geneb]

You're quite welcome William. I'm happy to do it.

When time permits I'm going to craft up a tiny board that will host 16 high-current transistors so that much higher loads can be driven - as much as 1A per channel anyway.

I have to thank Leo for bringing this up - it just never occurred to me. No digital output board I've ever seen (including the top of the line commercial ones) have ever mentioned this particular max limitation. As the board stands right now, it's fantastic for driving LEDs and 7 segment displays, but needs a bit of help for those higher loads.

g.

[Mike.Powell]

Gene,

For higher outputs consider an IRL520N. It's cheap (~60 cents IIRC), handles up to 10 amps, and can be driven from a logic signal. I've used it in a switching dimmer.

[geneb]

Thanks for the tip Mike. I'll get some of those ordered soon.

g.