Minimal size 5V/100mA power supply

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Why not switch to LCD?

Are there tiny LCDs available? Like the size of one-digit 7seg indication? I've seen but never used two-rows 40 signs (or something like that). I've seen also on some catalogue 2 digits + a sign LCD, but I think it is too big for my form-factor ;)

Run on 3 volts with no regulator from alkaline button cells or AAA. If you need regulation use it for the sensor alone - lower voltage almost always equals less power. Or use some of that pic power and monitor the supply voltage and correct the sensor output for low supply.

Try the duty cycle idea, that should cut the power in half. Do you have only one single digit 7 segment display?

I experimented a bit with some leds. I needed an all light readable indicator from next to no power - set the controller to output a PWM signal to charge a 10 volt cap (small inductor flyback booster with only 6 parts) (~10 ma 3 V) then dumped that in one flash that I gated on and off with the controller. That should also work with a display because of persistence of vision. You won't have a continuous monitor of temperature just a burst of light at (long) intervals to save power.

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--- Yes, but they can be tricky to find.

Best bet is probably to Google "static LCD glass" ;

I found:

and:

There must be many more.

-- JF

100 mA is a huge amount of current for an LED. Are you using an older, low-efficiency part?

Duty-cycle modulation will drop current and apparent brightness together.

LEDs keep getting better. Single led's are now bright at 1 mA. We tried some new Osram surface-mount parts and, in room light, a couple of the colors lit visibly, in room light, a 2 microamps.

John

That is really astonishing... Which colors?

Regards, Bob Monsen

I got out an old kingbright 7 segment display with 4 digits. It offers a multiplexed output using a common anode. To get reasonable brightness, it required 10mA per segment, meaning the most current it would need at one time is 70mA.

However, when you multiplex it, you end up with brightness which is roughly proportional to the on duty cycle. So, being on 1/4 of the time means you it might need more current per segment.

Because of this, I don't think you'll be able to use a coin or button cell, since they have too much internal resistance. You could go with an AA alkaline cell and a boost SMPS, or multiple AA cells. A boost switcher would give you a regulated output, and waste less than a 9V and linear regulator. There are also small rechargeable cells. Check this out:

A 1/4 AAA is 10.5 by 14 mm. Not too bad.

Regards, Bob Monsen

How about using a LCD display instead?

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The power consumation is so high (100mA), becouse the 7segment indication is not a single LED, but 8 LEDs (including the decimal point). That makes 12.5 mA current by each LED. Also I've put small resistors - only 200 ohms for better reading, but I will change them with 440 ohms. @default: I didn't understood your power supply device. Can you attach some schematics? I've checked that page

ard.htm but the smallest LCD is still too big - 21.08x18.95x2.80 The LED I'm currently using (SA36-11SRWA) is 14x5x8. The matchbox is roughly 30x50x15

Regards, Ivan.

or maybe even an oled depends on your price bracket, but you can get small OLEDs:

or even an OLED with a parallax propeller micro on board:

It will fit your case, and be a lot less power than the LED displays.

Cheers Don...

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Don McKenzie

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