I'm working on an IR transmitter that I just cannot get going.
I'm using a TSOP 4838 as the receiver connected to a 74 series inverting gate so the "receiving IR indicating LED" comes on when the TSOP receives a signal (active low output, so I had to invert it).
The receiving side works fine. I can go all the way across the room with a TV remote and make my indicator LED flash all day long.
My transmitter is another story.
I'm using an astable 555 generate a 38khz square wave (My schematic attached shows a fixed resistor, but its actually a pot adjusted around 8K). Since the TSOP doesn't like continuous pulses, I've set another 555 up with its output connected to the "38khz wave" 555 (connected output from the "pulse control 555" to pin 2 [trigger] of the 38khz 555).
See schematic in attachments.
I've calculated the following info about my pulse generator 555:
Frequency in Hertz: 496.5517
Duty Cycle: 60.00%
Mark Time (O/P High) 1.20582ms
Space Time (O/P Low) 0.80388ms
R1: 1,000,000
R2: 2,000,000
C1: 0.000000000580 (580pF)
This should generate -- in terms of 38khz cycles:
About 46 cycles of 38Khz IR LED off
About 31 cycles of 38Khz IR LED on
This seems to be well within the requirements of the TSOP4838.
I don't have anything to measure frequency, so I have a feeling that the way I've cascaded the 555s I'm not actually getting a 38Khz signal pulsed on for 31 cycles. The reception indicator LED seems to agree here.
That little Circuit Sim applet I took a shot of to attach does confirm my "pulser 555" frequency, but will not display a reading of the second 555. I'm wondering if it is actually generating a pulsed 38Khz output.
Any help is appreciated. Thanks!
I'm using a TSOP 4838 as the receiver connected to a 74 series inverting gate so the "receiving IR indicating LED" comes on when the TSOP receives a signal (active low output, so I had to invert it).
The receiving side works fine. I can go all the way across the room with a TV remote and make my indicator LED flash all day long.
My transmitter is another story.
I'm using an astable 555 generate a 38khz square wave (My schematic attached shows a fixed resistor, but its actually a pot adjusted around 8K). Since the TSOP doesn't like continuous pulses, I've set another 555 up with its output connected to the "38khz wave" 555 (connected output from the "pulse control 555" to pin 2 [trigger] of the 38khz 555).
See schematic in attachments.
I've calculated the following info about my pulse generator 555:
Frequency in Hertz: 496.5517
Duty Cycle: 60.00%
Mark Time (O/P High) 1.20582ms
Space Time (O/P Low) 0.80388ms
R1: 1,000,000
R2: 2,000,000
C1: 0.000000000580 (580pF)
This should generate -- in terms of 38khz cycles:
About 46 cycles of 38Khz IR LED off
About 31 cycles of 38Khz IR LED on
This seems to be well within the requirements of the TSOP4838.
I don't have anything to measure frequency, so I have a feeling that the way I've cascaded the 555s I'm not actually getting a 38Khz signal pulsed on for 31 cycles. The reception indicator LED seems to agree here.
That little Circuit Sim applet I took a shot of to attach does confirm my "pulser 555" frequency, but will not display a reading of the second 555. I'm wondering if it is actually generating a pulsed 38Khz output.
Any help is appreciated. Thanks!
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