Flashing LEDs as a coarse ADC (supply volts monitor)
Tubular
Posts: 4,706
Here's an initial measured curve for Kingbright flashing LED as discussed previously in deSilva's VCO thread.
The obvious use for this is for battery/psu monitoring - replacing the standard power-on LED with something that has the same number of PINs but lets your Prop program sense the incoming (unregulated) supply voltage.
82 ohm series resistor to ground - to give 3.7 volts peak into the prop at ~14v max Vin (input range of say 5-14 volts).
Vin ---|>|----Prop----^v^v^v----GND
For lower ranges use a larger resistor.
Or for wider range invest in a second series resistor into the prop input to drop (like 5v interfacing).
Peak flashing LED current is 8/25/43 mA at 3.5/5/12 volts respectively. But duty cycle is around 25% so average current is approx 2/6/11 mA.
I'll follow up with temperature stability once I have my test rig completed.
Post Edited (Tubular) : 2/26/2008 5:20:39 AM GMT
The obvious use for this is for battery/psu monitoring - replacing the standard power-on LED with something that has the same number of PINs but lets your Prop program sense the incoming (unregulated) supply voltage.
82 ohm series resistor to ground - to give 3.7 volts peak into the prop at ~14v max Vin (input range of say 5-14 volts).
Vin ---|>|----Prop----^v^v^v----GND
For lower ranges use a larger resistor.
Or for wider range invest in a second series resistor into the prop input to drop (like 5v interfacing).
Peak flashing LED current is 8/25/43 mA at 3.5/5/12 volts respectively. But duty cycle is around 25% so average current is approx 2/6/11 mA.
I'll follow up with temperature stability once I have my test rig completed.
Post Edited (Tubular) : 2/26/2008 5:20:39 AM GMT
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Comments
This is cool - Is this the Kingbright L36BSRD-B flashing LED you mentioned in the "VCO as ADC" post started by deSilva?
Rgds, David
There are newer Kingbright ones WP36B* WP56B* etc which have basically the same characteristics.
www.kingbrightusa.com/category.asp?catalog_name=LED&category_name=Blinking%20LED&page=1
Be aware the Kingbright "forward current" is a peak value and they have a duty cycle just below 25% giving the average values mentioned above.
Some other flashing LEDs have reduced voltage range (say 4 to 7v), and there are other boring ones whose frequency is designed to be absolutely constant (+/- .02 Hz!) I hope to test others a few weeks down the track.
Post Edited (Tubular) : 2/26/2008 5:58:02 AM GMT