Problem in uln2803

[Jpsinghbrar]

I hav problem with inveter action of uln2803 . Input to it is from 8051 port (with approx 1V) . I have connected each output of uln2803 to 12V through 10k resistor to get inverter action.But m not succesful. Otherwise if high input to uln2803 is above 2.5V ,only then inverter action is obtained. pls help me in my project so that i can get inverting action even at input voltage lower than 1V.

 

[alec_t]

Why is your 8051 output voltage (1V) so low?

 

[panic mode]

ULN2803 expects TTL levels. input is "1" when above 2.5V and "0" when below 0.8V. anything in between is not defined. but if the signal is changinh (you get bunch of transitions) your multimeter may not display correct value

 

[ronsimpson]

the 8051 does not pull up good. Connect a pull up resistor on the output of the 8051. 1k ohms.