power-optimized self-calibrating PWM driven light-sensing electro optical circuit


Despite the long title, this is nothing more than the simplest night-light imaginable... a single LED hooked up to a Picaxe; not even the current limiting resistor of the typical "hello world" intro project. It's amazing that even the simplest Picaxe chip now available can be programmed into a 1000+ point datalogger, a clock, or a even thermometer, with no additional components, and running off of nanowatts scavanged from "dead" AA batteries, at a cost of less than $3 per build.

I'm late to the party in using the new M2 parts; but I love seeing how software and silicon keep replacing hardware: Timers to replace real-time-clock chips, internal pull-up resistors that take the place of external components, capacitance sensing routines that eliminate the need for buttons. Eventually, everything almost becomes a matter of software.

Just like some amateur radio operators go down the QRP route to see how far they can communicate on a few milliwatts, I like working with a minimalist machine consisting of a single input bit, single output bit, and the highly evolved Turing machine that is the Picaxe 08M2. To go from yesterday's "hello world" project, to todays self-calibrating nightlight, to this weekend's data-logging clock is just a matter of software. Can anyone share some pointers to others with this minimalist obsession?

Project details at http://corticalcafe.com/picaxe_simple_nightlight.html


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Can anyone share some pointers to others with this minimalist obsession?
Normally we catch then quickly and have them put some place where they can't do any harm :)

lbenson gave us a low-power reference design which I believe is still flashing LED's and approaching its five years anniversary ...


There are a few others on the forum who have strived to get microamp consumptions out of PICAXE designs.

And then there's the 'cutting legs off chips and still having things work' field which is always good for entertainment.

I particularly liked your warning on your project page - That's the spirit !

And don't forget there's always the Official PICAXE Project Gallery where you can showcase projects ...



Thanks for these replies. Good stuff!

I've seen many examples of using using LEDs a sensors over the years. But the idea of having these minimal devices interact and respond to each other is genius. I don't see wilf_nv's project online, but just the idea gives me plenty to think about.

Btw, I noted that when the 08M2 was in low-power, just disconnecting the batteries for a few seconds wasn't enough to reset the device. I had to keep them disconnected for > 15 seconds and/or short the power leads. I'm attributing this to the minimal power consumption (32uA at 1.8V if I'm reading the spec sheet correctly) combined with stray capacitance. Is this a reasonable explanation? I'm sure that this can be exploited in some way, though I don't quite know how/why. Have you seen anyone use this effect intentionally?