I have a 555/4017 board that I'm trying to drive a ULN2803 to power an LED array. Is the 4017 so "weak" that it cannot signal the ULN? I get no response from my circuit, past the indicator LEDS on my chaser board.
That will depend on of how you use(connect) itBe aware the 2803 will not drive high. It needs a pull up.
If you are connecting the LED's to the 2803 outputs the same way as in the CD4017 connection in your schematic, they won't light up. This is because the ULN2803 only sinks current.This is my board, which is already soldered onto perf. I'm using it's LED path to connect to the 2803's inputs (on bread). Nothing happens. I'm wondering where the 9V power on the perf went! Hardly anything is left to hit the 2803, I guess.
Yes. I understand the 2803 is not a power source, only a relay to a ground for each LED. I have a bank on LEDs in parallel with a 300 ohm resistor at each output of the 2803 with a separate low volt, high current power source for the array. (9v at 2.2A)If you are connecting the LED's to the 2803 outputs the same way as in the CD4017 connection in your schematic, they won't light up. This is because the ULN2803 only sinks current.
Do you understand the difference between sinking and sourcing ?
In a nutshell....Can you please post your complete schematic as built ?
If the CD4017 is connected directly to the ULN2803 inputs and is not broken, the CD4017 output voltage should be near it's V+ supply when the CD4017 output is high and in a static condition.
But if chasing, you will get a lower reading.
As referenced, no, no resistors for the LEDs on the perfboard. I will add the appropriate rating (~330) tonight.As mentioned earlier, you have LED's connected to the CD4017 outputs without current limiting resistors. You must use current limiting resistor for those LED's also.
Those LED's are lighting properly, correct?
Were is the ground connection on the 2803 ?
The C (common) connection goes to internal diodes. It should be on V+. -- Look at the datasheet.
But, if connected as shown the LED's in the array should be lit constantly through those diodes.
Is the LED array polarity correct?
Thanks for your help. I've annotated my layout to make it more descriptive. When I finish adding the resistors to my perfboard, I'll post the result.I see now that the C could be a G, so that is correct. Your understanding of the ULN2803 is accurate.
Common anode wiring of the array is correct.
It's possible the LED's on the CD4017 without limiting resistors are preventing the Darlington's in the ULN2803 from turning on completely.
The ULN2803 is designed to work with TTL voltages, roughly 5VDC. You are using a 9VDC power supply which is outside its designed range (to the best of my knowledge). I suggest using a ULN2804 which is designed to work with 6-15VDC.I think according to the specs on the 2803, 2v is the min input to drive it?
The 2803 and 3804 differ only by the series resistance in the input(Base on the darlington transistor) The 2803 use a 2.7K resistor, and the 2804 use 10.5K resistor. By adding a series resistor to input of a 2803 you can use the 2803 safe at higer voltagesThe ULN2803 is designed to work with TTL voltages, roughly 5VDC. You are using a 9VDC power supply which is outside its designed range (to the best of my knowledge). I suggest using a ULN2804 which is designed to work with 6-15VDC.
Also note CMOS ICs and 555's are inherently noisy and may affect operation of the other. Add a 0.1uF ceramic capacitor across the power leads of the 4017. Add a 0.1uF ceramic AND 1uF electrolytic across the power leads of the 555.
Are you using two sets of LEDs - one on the output of the 4017 and one on the output of the ULN2803 as shown in your schematic? If so, why?
What is the forward voltage and current rating of your LEDs? If you're using two different types of LEDs, please post the specs for both.
Post a picture of your set-up - we might be able to spot something there as well.
I have a bank of LEDs on my perfboard as a monitoring tool. Orange? LEDs I'm assuming 3.4v FV. I had them laying around. The output array will contain 48 white LEDs (3.4v).The ULN2803 is designed to work with TTL voltages, roughly 5VDC. You are using a 9VDC power supply which is outside its designed range (to the best of my knowledge). I suggest using a ULN2804 which is designed to work with 6-15VDC.
Also note CMOS ICs and 555's are inherently noisy and may affect operation of the other. Add a 0.1uF ceramic capacitor across the power leads of the 4017. Add a 0.1uF ceramic AND 1uF electrolytic across the power leads of the 555.
Are you using two sets of LEDs - one on the output of the 4017 and one on the output of the ULN2803 as shown in your schematic? If so, why?
What is the forward voltage and current rating of your LEDs? If you're using two different types of LEDs, please post the specs for both.
Post a picture of your set-up - we might be able to spot something there as well.
Kind of overlooked that. So driving the 2803 in series AFTER the LEDs and grounding them within the 2803?? Or just removing them....Did you still connecting the 10 LEDs from the output of CD4017 to GND?
If you want to try the ULN2803 then you better take the LEDs away.