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The only problem with leaving it in is it adds a voltage drop. It is only really necessary on a pin which can be configured as either an output OR and input. You wouldn't need it on pins 10-13 & 15. That said, the safety resistor may save your ass (and pins 10-13 & 15) if you connected it to 12V or something.It refers to the 330 resistor as a "safety resistor". Are you sure I should leave it out?
It should be bright enough at close range. How far away is it going to be? Be sure to use a transistor with the same peak wavelength sensitivity as the LEDs peak wavelength output. What colour is the LED you have? The datasheet you posted covers 3 different colours and thus 3 different peak wavelengths.I plan to mount the photo transistor right next to this led. Would I need to add a transistor to the circuit or is the light from the led bright enough for the photo transistor to detect?
It should be bright enough at close range. How far away is it going to be?
What colour is the LED you have? The datasheet you posted covers 3 different colours and thus 3 different peak wavelengths.
Yes, I did see that one. It doesn't look like it would be a standard photo-transistor, but rather a fiber optic transmitter going by similar part #s on **broken link removed**. Everlight's website doesn't list a datasheet for the PLT131, so I would avoid it.Mouser has a photo transistor that has a 660 nm Peak Wavelength:
EL-PLT131/6 Everlight Photodetector Transistors
The sensitivity is a curve which looks like a steep mountain. So it's "off-colour" sensitivity could be anywhere from 50% to 5% of the peak sensitivity or less.How critical is it that the peak wavelength of the transistor match the wavelength of the led?
Yes. See above. What are you try to accomplish anyway? Will a optocoupler or photo-interrupter not work? Why the need for two discreet devices?If the wavelength of the led is different than the transistor, will the transistor detect the light?
Ah. I see now why you chose a bi-colour LED.
An AC opto coupler would be the solution for you. The AC opto couplers have two back to back LEDs just like your bi-colour LED does. The 859-LTV-814 from mouser should work in this application. You could connect it like this:
Yes, it'll work perfectly. It will also work no matter which polarity is applied to the LED input. I chose it for this feature because of your reversing DC motor.My power source is DC. Would an AC opto coupler work with a DC power source?
What is the voltage across the motor at this point?This problem seems to occur when the voltage on pins 1 and 2 is below 1.18v.
What is the voltage across the motor at this point?
How is the motor controlled? ie: Is it controlled via a PWM motor speed controller or is it being fed straight DC?
You could reduce the resistor value to increase the LED current in the opto if the motor is running on straight DC. I wouldn't go beyond 30ma LED current as the max for the LTV-814 is 50ma.