originator
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I have a processor at 3.3 sending i2c commands to a PCF8575 16 bit 1/o expander which is also at 3.3. There are two ULN2803's attached to the 16 outs of the PCF8575. When an output is turned on, the voltage on any/all 16 pins is .93VDC. The ULN2803 is to sink a relay that has 5volts on it. The .9V is not turning on the transistor pair to sink the relay coil. Does this make any sense to anyone why the output is low?
Thanks
PS the schematic shows 12v on the relay but it is 5.
EDIT sorry for the post, the 8575 part is not a full power output s I was told. It is is at full power for a gew micro seconds only, then drops to low power. I added pullups and solved it.
Thanks
PS the schematic shows 12v on the relay but it is 5.
EDIT sorry for the post, the 8575 part is not a full power output s I was told. It is is at full power for a gew micro seconds only, then drops to low power. I added pullups and solved it.
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