## IR Transmitter circuit.

 IR Transmitter circuit. From: Sam Varshavchik - 2001-08-16 22:20:00 ```Anyone care to comment on the following rough circuit for a transmitter I intend to build, perhaps saving me the trouble of dealing with a fried port? It's signalled slightly differently than typical circuits, so I probably won't be able to use it with lirc out of the box, but I'll cross that bridge when I come to it. I haven't checked, but if lirc keeps RTS pulled high while frobbing DTR, it might work if I reverse DTR/RTS designations on the following diagram. The basic problem I'm trying to solve is to be able to use a fairly long cable from the serial port, but still generate a strong signal. The sample circuit that's linked from lirc.org's page is relatively complicated, because it's trying to both charge the circuit and signal it with a single pin. I suspect that if a second pin is used to charge the capacitor, the circuit becomes much simpler: GND---------------+--------+------------------------+ | | | | \_/ | | --- | | | | 5-11V+----+ 5V | // | DTR ---->|-----| VR |------+---->|----/\/\/\/--| | +----+ I | | / | |/ | RTS ---->|--------------/\/\/\---------------+\ | | \ | | | +----+ VR is a 5 volt regulator, "I" is the transmitter. The way I figure it, no matter how much of a voltage drop I get from a long cable, I'll end up with a precise 5V. This should allow me to use the right resistor to get precisely the maximum amperage that the transmitter is rated for, then use RTS to switch the transmitter on/off through an NPN transistor. The transistor should be switchable with very little current, so all I need the resistor for is to cap the maximum current. I'm not sure if sticking another voltage regular before the resistor/transistor would mess up the signal timings. -- Sam ```

 IR Transmitter circuit. From: Sam Varshavchik - 2001-08-16 22:20:00 ```Anyone care to comment on the following rough circuit for a transmitter I intend to build, perhaps saving me the trouble of dealing with a fried port? It's signalled slightly differently than typical circuits, so I probably won't be able to use it with lirc out of the box, but I'll cross that bridge when I come to it. I haven't checked, but if lirc keeps RTS pulled high while frobbing DTR, it might work if I reverse DTR/RTS designations on the following diagram. The basic problem I'm trying to solve is to be able to use a fairly long cable from the serial port, but still generate a strong signal. The sample circuit that's linked from lirc.org's page is relatively complicated, because it's trying to both charge the circuit and signal it with a single pin. I suspect that if a second pin is used to charge the capacitor, the circuit becomes much simpler: GND---------------+--------+------------------------+ | | | | \_/ | | --- | | | | 5-11V+----+ 5V | // | DTR ---->|-----| VR |------+---->|----/\/\/\/--| | +----+ I | | / | |/ | RTS ---->|--------------/\/\/\---------------+\ | | \ | | | +----+ VR is a 5 volt regulator, "I" is the transmitter. The way I figure it, no matter how much of a voltage drop I get from a long cable, I'll end up with a precise 5V. This should allow me to use the right resistor to get precisely the maximum amperage that the transmitter is rated for, then use RTS to switch the transmitter on/off through an NPN transistor. The transistor should be switchable with very little current, so all I need the resistor for is to cap the maximum current. I'm not sure if sticking another voltage regular before the resistor/transistor would mess up the signal timings. -- Sam ```
 Re: IR Transmitter circuit. From: Sam Varshavchik - 2001-08-16 22:27:31 ```Sam Varshavchik writes: ... That didn't come out very well, did it? Let's try again. # GND---------------+--------+------------------------+ # | | | # | \_/ | # | --- | # | | | # 5-11V+----+ 5V | // | # DTR ---->|-----| VR |------+---->|----/\/\/\/--| | # +----+ I | | # / | # |/ | # RTS ---->|--------------/\/\/\---------------+\ | # | \ | # | | # +----+ -- Sam ```
 Re: IR Transmitter circuit. From: Jerome Kaidor - 2001-08-17 13:43:00 ```Hi Sam, As somebody already pointed out, your main problem will probably be head room for the regulator. If that does turn out inadequate, you might try a zener diode instead. These don't require any head room at all, although you still need a bit to deal with varying current demand from the load. ( And if the current demand from the load did not change at all, you could get by with no VR at all :)). I had a similar situation - I wanted LIRC to work through a fifty-foot serial cable. I punted and ran the transmitter off a wall wart. - Jerry Kaidor ( jerry@... ) > Sam Varshavchik writes: > > ... That didn't come out very well, did it? Let's try again. > > # GND---------------+--------+------------------------+ > # | | | > # | \_/ | > # | --- | > # | | | > # 5-11V+----+ 5V | // | > # DTR ---->|-----| VR |------+---->|----/\/\/\/--| | > # +----+ I | | > # / | > # |/ | > # RTS ---->|--------------/\/\/\---------------+\ | > # | \ | > # | | > # +----+ > > > -- > Sam > > > ```
 Re: IR Transmitter circuit. From: - 2001-08-17 10:39:16 ```Hi! Sam Varshavchik "mrsam@..." wrote: > Sam Varshavchik writes: > ... That didn't come out very well, did it? Let's try again. > # GND---------------+--------+------------------------+ > # | | | > # | \_/ | > # | --- | > # | | | > # 5-11V+----+ 5V | // | > # DTR ---->|-----| VR |------+---->|----/\/\/\/--| | > # +----+ I | | > # / | > # |/ | > # RTS ---->|--------------/\/\/\---------------+\ | > # | \ | > # | | > # +----+ Just some notes: Typical VR's need at least 7V at their inputs to produce a stable 5V. For your application you should consider large buffer capacitors. I guess there's a good reason why you switched the role of RTS and DTR. Christoph ```