Hi all,
I have a shift register 74hc595. This is driving a uln2003lv transistor array, that in turn drive relay coils.
The shift register is controlled by a microcontroller. I need to make sure that the shift register is high z on switch on si I don't get relays coming on.
From the truth table the output enable line must be high and master clear a low.
The output enable is also used to switch the data onto the shift registers by making the line low.
Can I tie a pull up to the output enable line for switch on I.e. making it high?
But my question is how to make it low?
Do I need a transistor and base resistor (also resistor from base to 0v) to keep transistor off at switch on. then the collector to vCC via pull up. Then switch this line low by turning in the transistor.
Is that the best method?
Sorry if this seems trivial to some of you, I just need some clarification.
Thanks,
Raj
I have a shift register 74hc595. This is driving a uln2003lv transistor array, that in turn drive relay coils.
The shift register is controlled by a microcontroller. I need to make sure that the shift register is high z on switch on si I don't get relays coming on.
From the truth table the output enable line must be high and master clear a low.
The output enable is also used to switch the data onto the shift registers by making the line low.
Can I tie a pull up to the output enable line for switch on I.e. making it high?
But my question is how to make it low?
Do I need a transistor and base resistor (also resistor from base to 0v) to keep transistor off at switch on. then the collector to vCC via pull up. Then switch this line low by turning in the transistor.
Is that the best method?
Sorry if this seems trivial to some of you, I just need some clarification.
Thanks,
Raj