G
Gary
- Jan 1, 1970
- 0
I am trying to steer the output of an infrared controller to one of eight
devices. For the steering circuit I've used a 74htc138. Each output is
connected to a pnp transistor (mpsa56) through a 5k resistor. The
transistor is used to supply 5V to the ir emitter. All 8 emitters are tied
together and into an npn transistor (pn2222a) that generates the pulses.
One of the outputs of the 138 is always selected providing 5v to the
appropriate emitter. Measuring the connection between the mpsa56 and ir
emitter I get 5v for the selected emitter and zero for the other 7. However
on a scope, I can also see the ir pulses at this connection on all of them.
I've used visible ir emitters and they do not light but the devices, on the
unselected emitters, can sometimes detect the pulses and react.
How can I isolate the other seven emitters?
Thanks
devices. For the steering circuit I've used a 74htc138. Each output is
connected to a pnp transistor (mpsa56) through a 5k resistor. The
transistor is used to supply 5V to the ir emitter. All 8 emitters are tied
together and into an npn transistor (pn2222a) that generates the pulses.
One of the outputs of the 138 is always selected providing 5v to the
appropriate emitter. Measuring the connection between the mpsa56 and ir
emitter I get 5v for the selected emitter and zero for the other 7. However
on a scope, I can also see the ir pulses at this connection on all of them.
I've used visible ir emitters and they do not light but the devices, on the
unselected emitters, can sometimes detect the pulses and react.
How can I isolate the other seven emitters?
Thanks