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OldMMUser
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Joined: 05/08/2014
Location: United States
Posts: 6

Posted: 07:01am 11 Aug 2014

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Hello,

I used my CGMMSTICK1 for this simple project:

5 n = 100
10 SetPin(1),1
30 GoSub 100
32 Print "LED Voltage is: ",Format$(v, "%.2f")
40 Pause 500
50 GoTo 30

100 avg = 0
110 For x=1 To n
120 avg = avg + Pin( 1)
130 Next x
140 v = avg/n
150 Return

My LED voltages, yours MAY vary!

No LED ~ 3.30 (Self Test)
Red ~ 2.54
Yellow ~ 2.58
Green ~ 2.61
Blue ~ 2.90
White ~ 2.92
UV ~ 3.09

2014-08-11_171258_LED_CIRCUIT.zip

Test those LED's in your junk box! Reversed, open or shorted LED won't hurt this.
Edited by OldMMUser 2014-08-12

OldMMUser
Newbie

Joined: 05/08/2014
Location: United States
Posts: 6

Posted: 07:28am 11 Aug 2014

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Hello again,

Please note that if you use this setup with a "flickering" yellow LED
used in "Electronic Candles" it makes a 'pretty good' hardware random number
generator!

Enjoy!

WhiteWizzard
Guru

Joined: 05/04/2013
Location: United Kingdom
Posts: 2927

Posted: 08:18am 11 Aug 2014

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Nice 'discovery' regarding the random number generator!

Going to use your discovery to select my next lottery numbers

CircuitGizmos

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Joined: 08/09/2011
Location: United States
Posts: 1427

Posted: 09:19am 11 Aug 2014

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Nice! That is an interesting approach - determining likely color based on voltage drop.

Micromites and Maximites! - Beginning Maximite

bigmik

Guru

Joined: 20/06/2011
Location: Australia
Posts: 2946

Posted: 08:24pm 11 Aug 2014

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Hi OldMMuser,

A novel idea but I wonder about your logic of having the Analog Input at the junction or R1 and R2.. Should it not actually be at the junction of R2 and D1 (at D1's Anode)? That would possibly explain why your voltages are a bit higher than I would have expected them to be about 0.8v lower than what you show there.

Take for instance a `standard' RED Led of 1.7v forward voltage that means that your 2k (2 x 1k) resistor would drop the other 1.6v.

Using Ohms law: (V=IR) then 1.6/2000 = .0008A or 0.8ma

With 0.8ma flowing in R2 (and R1) your Analog input would be 1000x.0008 or 0.8V higher than the actual drop at the LED..

Take 0.8 off your RED led reading and guess what ... you have 1.74V

I would change your circuit to read at the junction of R2 and D1 instead then you will read the actual forward voltage of the LED.

Now another point, I am not certain but the forward voltage may change slightly (not dramatically) at a higher current draw.

Anyway good Idea, I like it.

Regards,

Mick

Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<

hitsware
Guru

Joined: 23/11/2012
Location: United States
Posts: 535

Posted: 07:03am 12 Aug 2014

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> the forward voltage may change slightly
> (not dramatically) at a higher current draw.

Right. I use LEDs to bias amplifiers, and can
adjust the voltage (to some extent)with the
value of the resistor feeding it.

bigmik

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Joined: 20/06/2011
Location: Australia
Posts: 2946

Posted: 04:50pm 12 Aug 2014

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Hi Hitsware,

hitsware said
Right. I use LEDs to bias amplifiers,

Aren't LEDs a bit `noisy' for use in an amplifier or is that not an issue these days with more modern manufacturing processes?

Regards,

Mick

Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<

hitsware
Guru

Joined: 23/11/2012
Location: United States
Posts: 535

Posted: 12:47am 13 Aug 2014

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Bypassed with a cap. Plus the advantage of the right choice of voltages.
I use them in class AB output stage where noise is not so critical, but have seen them used in even phono preamp stages.

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