Help with an obp704

Sticky

Hi I wonder if someone can show me where I'm going wrong with an opb704. I setup a breadboard to test it but I can't seem to get a high and low reading off of it. Any help is appreciated.

Franklin

Can't see all the leads in the photo. How are you powering it?

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- Stephen

kwinn

As shown in schematic "Input" should be low when pointed at reflective surface or light, high when dark non-reflective circuit.

The led and phototransistor can be tested separately.

The voltage across the led should be around 2~2.5V.

Disconnect the led to test the transistor.

The "input" point on the phototransistor should be high if the sensor is covered to keep it dark, and low if exposed to light.

If the "input" point is always low try a lower value resistor like 10K or 4.7K instead of the 10K

Sticky

I'm powering the circuit with a regulated 5 volts. I had this working with a stamp and another breadboard but a lead broke and I had to resolder it, and I changed the breadboard a bit in between and now it doesn't work - bah! I'm using 43k I believe instead of the 47k in the schematic I don't think it makes a difference. I'm trying to read from the input through a meter to a ground, is this right? I use it with a "pie" like circle with alternately dark and light "slices". It really worked well.

I tried changing the resistor on the transistor to 4.7k but it didn't seem to help. I'll try the other debugging techniques also, like deactivating the led. I just constantly get a high reading off the "input".

Sticky

Thanks kwinn - The led and phototransistor can be tested separately.

The led's weren't functioning on all three of the 704's - I used an ir led to test and the receivers are ok. Guess soldering the leads fried them.