Nedd help with visible light photo detector circuit

[Buzzed]

Hi guys I’m a newbie residing in Ohio. I fly MikroKopters which is what brings up my question. Onboard my Hexa is a small GPS. The GPS uses a green LED that is normally on when powered up and starts to flash when 3D lock is achieved. Herein lies the problem, the LED is almost impossible to see in bright sunlight under the smoked dome of the MikroKopter and impossible to see when flying.

What I would like to do is build a simple, lightweight, compact photo-detector that can see the LED and mimic the flash pattern. Then it can be used as a switch to power up a strip of flexible LEDs that will be mounted on one of the motor support arms that can easily be seen when flying.

The target voltage is 12 – 14.8 volts dc which is the voltage of the flight pack and also the voltage for the flexible LED light strip.

Any help you guys can afford would be greatly appreciated by me and the MikroKopter community.

 

[user_88]

What is the possibility of directly accessing the electrical connection to the green GPS LED?
You might have to open the GPS case ... snip and splice ...
The idea is to achieve a direct electrical signal to activate the external LED strip.

The use of a photo sensitive optical connection could require a certain amount of experimentation ... to get a solid activation signal.

 

[Buzzed]

I'm looking for an solution that other MikroKopter pilots can use for their birds without causing them to have GPS problems because of a botched solder job to their PC boards. Some of the guys purchase RTF Kopters because they can't or don't want to solder boards.

 

[user_88]

Here are some typical photo sensitive circuits ...
Plan on trying a few parts out ... to get everything to work right.
**broken link removed**

 

[Reloadron]

Going the CDS photo cell route would involve placing a maybe CDS photo cell right on the existing LED then using a small circuit along the lines of those linked to by User_88. A simple 5 pack of assorted photo cells to experiment with can be had at a local Radio Shack just like these.

Likely the best option would be if the leads of the existing LED were available. This would allow the use of a niice simple Opto-Coupler design which could drive additional, more visible string of LEDs keeping the parts count and weight down.

Ohio? Sitting here in the Cleveland burbs myself.

Ron

 

[Buzzed]

Hey Ron I'm south of you near the Canton Football Hall Of Fame.

I actually found and ordered a nice assortment of the CDS cells at Electronic Goldmine. Never ordered from them before this but the prices were right.

I appreciate all the tips guys.

 

[Reloadron]

Cool, when they arrive I would try working from the circuits user_88 linked to. Using assorted CDS cells place them over your existing LED and measure the light and dark resistances. What you are looking to do should not be that difficult getting a little creative.

Ron

 

[Buzzed]

Once the cells arrive I'll give it a try and get back to you with the results Ron.

 

[Reloadron]

Yeah, let us know how it goes. Should be a nice project and if it works well, something others can use.

Ron

 

[Buzzed]

I believe I now have the parts that I need to put this together however I'm unsure on the LM339 pin numbering. Can you guys look at the right circuit and tell me if the ones I have numbered are correct and what the other two are?

 

[Joe G]

power (V+ and V-) ground

 

[Buzzed]

Joe guess I should have been more specific. What are the pin numbers for the power (V+ and V-) ground that you mentioned? Would that be 3 and 12

 

[Joe G]

https://www.electro-tech-online.com/custompdfs/2012/01/lm339-n.pdf datasheet= page 17. 12 is gnd 3 is v

 

[Joe G]

also, just food for thought, if you only need the one comparator, they do make single comarators. smaller size =less weight.

 

[Buzzed]

Joe that's actually pretty funny as I put the circuit together and not only does it work but it works quite well. And the next thought I had was geez I wonder if I could make this package smaller...

So what would I use to substitute for the LM339 considering the simple circuit that I'm using?

Since I'm switching 12 volt DC flexible LED strips I guess it would also be a good to know the milli-amps that the circuit might handle without going poof, any guess?

 

[Joe G]

i use the lm2903 for breadboarding just a 8 pin (2 comps vs the 4 ) half the size, surface mount i use the single comp

 

[Reloadron]

Pin 12 is Ground and Pin 3 is your Positive supply voltage. Pin 6 is correct and a (-) inverting input and Pin 7 is correct and a (+) Non-Inverting input. This is a data sheet for the LM339 chip, it should help. Also keep in mind, this chip contains 4 comparators in a single chip. You are using 1/4 of the chip. For things to work correctly all unused inputs should go somewhere. So tie all the inverting inputs pins 4, 8, and 10 to ground and the non-inverting pins 5, 9, and 11 to your positive supply.

Ron