Kitz Forum
Chat => Tech Chat => Topic started by: sevenlayermuddle on April 21, 2020, 10:39:44 AM
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Since I got a smidgen of encouragement in a different thread, I'll now bore anybody opening this post, with one of my recent endeavours
It's nearly 20 years since I dabbled much with diodes and things. But a few months ago I decide to build a very simple device, a flashing LED that would hang inside the side window of the garage, that would remind me that the front door of the garage is open. It would be based on an ancient IC, the venerable '555' timer. Just a few components and a scrap of vero board were all I needed.
Then started to think of refinements and specific requirements, and got a bit carried away...
1. Assuming door open no more than 4 hours a day, it should run for 1 year on 3xAA cells, with consistent intensity throughout.
2. In between flashes, when the LED is off, it should use the LED as a photovoltaic sensor, and thus modulate the intensity according to daylight levels, by adjusting the duration ('on time') of each LED blink.
3. It should warn me, by dramatically reducing the flash interval, when cell voltage dropped below 1.0V.
4. It should use only 'old' analogue technology, so I can debug with not much more than a DVM.
I'm sure a currently professional designer would find much to criticise but I eventually breadboarded a circuit that worked reasonably well. Unfortunately it now comprised not just the 555 timer but also 9 discreet transistors, 25 passive components, and a couple of trimmers for tweaking the light-sensing characteristics. Putting all this together on a scrap of vero board was much less appealing. :D
Enter two wonders of the world, about which I knew nothing last time I dabbled....
Free schematic and PCB design software, that runs on Apple's Unix-based MacOS, among other platforms.
https://www.kicad-pcb.org
Cheap Chinese PCB manufacture.
For $4.90 (plus shipping), I get five double-sided PCBs, with silk screen and solder mask.
https://www.elecrow.com/pcb-manufacturing.html
PCBs designs now submitted, awaiting manufacture. I have tried to attach a couple of screenshots to at least show what I am expecting. Hope these show, I don't post many pics!
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I shall have to keep careful watch, on eBay, for some Chinese supplier to start selling complete and working copies of your design. :-X ;)
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::)
It’s also been suggested I should have the PCB X-rayed, to check for concealed surveillance chips.