Logout Register. Testing darlington pair IC? Initial test was to setup a simple diode circuit. All is good, the LED lights up, with a small python script to change state on pin Simple Diode Compressed. You do not have the required permissions to view the files attached to this post.
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Logout Register. Testing darlington pair IC? Initial test was to setup a simple diode circuit. All is good, the LED lights up, with a small python script to change state on pin Simple Diode Compressed. You do not have the required permissions to view the files attached to this post. Last edited by Schorschi on Sat Mar 16, pm, edited 1 time in total.
Re: Testing darlington pair IC? Sat Mar 16, pm I've been staring at your pictures and can't quite work out what you're doing.
Then C1 goes to the LED and resistor? You've also put 3v3 into the chip common? If you look at the data sheet it only feeds reverse-biased diodes - useful for relays and such like. Now am I right in thinking the other end of the LED-resistor chain goes to ground?
If so, that's your problem The darlington pair acts like a switch, connecting C1 to ground when B1 is taken high. So you need to connect the LED-resistor chain to a power source such as 3v3. Sat Mar 16, pm I walked away for a while, and then went back and googled use cases of ULNA and various examples. One specific example itemized that C1 is GND side, not power side. Thus, I realized that the darlington pair logic is different than I first realized. C1 connected to the diode circuit GND. Power goes from source, in this case Pi pin BCM 1.
This configuration works. The above issue resolved, next I wil add relay control behind the diode, so I can fire the relay coil as I always planned. Sat Mar 16, pm Looks like you've grounded both sides of the led to me. Pin 9 is GND. The way these work, when the input side gets a high signal, it connects whatever is on the output side to GND.
Wed Mar 20, am Thanks for the explanation! It closed the loop in my understanding. And yes, I will in the final design, drive a 4 channel relay for one project, and in other project a 8 channel relay.
Everything is working now, including driving the relay with a LED per channel so I can see the actual signal from Pi to relay from across the room. Some GPIO pins default to high or low depending on the distribution of Linux I have been using Fedora, since I was already familar with it and reading Gordon's blog, on how the default behavior of GPIO pins state at boot can be rather odd!
Some pins default to high versus low, on boot of Pi. But I found a few pins that are consistent, on Pi power up, so now I just need to practice my soldering have not done it since my university days, when I used to build custom cables as needed. Jump to. Board index All times are UTC.
Using an input circuit with a total input capacitance of 2pF, the input current noise density is 4. With lower capacitance, noise and bandwidth improve further. This product has been released to the market. The data sheet contains all final specifications and operating conditions. For new designs, ADI recommends utilization of these products.
ULQ2804A Datasheet PDF
ULN2803AP = ULN2803