I'd like to build a scheme like at this page: Arduino : use a shift register (74HC595) and a transistor array (ULN2803) – Erwan's Blog
But I have a strange problem: output voltage on ULN2803 pins is about 0,61 V... I power it from arduino, which is connected to my PC via USB. What am I doing wrong? Or maybe this IC is burned?
I checked it several times and I'm sure that 9. pin is connected to GND and 10. pin to VCC. I also check input voltages which is about 4.6 from +5V line from Arduino.
Em... so how can I light a diode up with it? This voltage is too low... And in the scheme all diodes are connected this way an this probably works. What am I doing wrong?
It doesn't supply voltage... It completes the circuit to ground...
[u]Here[/u] is a regular transistor in a similar circuit. Note how the power (positive voltage) is applied to the solenoid coil. Current flows when the transistor turns-on and pulls the other coil connection to ground.
Asmox:
Em... so how can I light a diode up with it? This voltage is too low... And in the scheme all diodes are connected this way an this probably works. What am I doing wrong?
Low is good.
That darlington array is just a bunch of switches to ground.
There should ideally be NO voltage across a switch.
A darlington is a bad switch. It can even drop up to 1.5volt across the switch.
Your supply needs to be that much higher to compensate.
That diagram uses a 6volt battery to light up common 2volt LEDs.
Enough overhead (~4volt) to allow for the drop of that darlington and the current limiting resistor.
Leo..