I have a k8055 board connected to a pc via the usb port.
On the clamp i have connected +12 and GND to GND.
Although the out ports are working correctly the voltage on the out ports is 0v when off and 0.6V when on. The powersupply is ok.
Is the ULN broken?
Some help would be appreciated.
Thanks.
Your ULN2803 is not broken.
The CLAMP is intended to connect to the positive supply voltage. This is to protect the output transistors of the IC4 ULN2803 against the voltage spikes generated by inductive loads (relays) when the coil current is turned off. You have done this connection OK.
The outputs of the ULN2803 are open collector. See the “PARTIAL SCHEMATICS” on the datasheet of the ULN2803.
To get some good output voltage swing from the digital outputs you have now to add a pull-up resistor (1k to 10k) from each of the output terminals to the +12V. See the example diagram on page 19 of the manual.
You are right.
Thanks a lot.