Hi,
I am working on a project in which I am driving a 8x8 matrix of electromagnets using 74HC595+ULN2803 combination, my problem is I should also reverse the polarity of them individually, having an H-Bridge for each output will not be an option since it's in matrix, but I am trying to have two matrix circuits one for positive and another one for negative so that I can drive selected electromagnet on decided polarity, here my problem is how can I switch between the power source from different ULN2803 legs? or is there any other way I can achieve the solution?

Thanks in advance,
-Prabhu

 

A schematic always helps.

To reverse polarity you have 3 options:
1. two coils in one magnet
2. an H-bridge
3. a Halfbridge and a Highside/Lowside driver.

 

If you A) are limited to a UNL2803 that switched current to ground, 2) have power to waste and Z) can use a series limiting resistor...

The current in the resistor gets wasted but results in each coil getting driven in both directions.