Hi there,
I am trying to build an IR receiver from the ground up using the RC-5 protocol. I am aware of components such as the TSOP382 (IR receiver) that does this all in a neat little package, however, I am trying to build a receiver from the ground up using a photodiode.
I have broken this problem into modules and I am using a tone-detector (LM567) to convert "the presence of a 36kHz tone" into a logic level. This is where I am having an issue. The tone-detector is incredibly slow to detect the tone and not only that, it goes through a period of oscillation before it settles after detecting the presence (or absence) of the tone.
To give some context, this is my first time working with a tone decoder, so I'm not sure if I have made a bad circuit or if tone decoders are actually this slow. Ideally, I want to match or come close to matching the performance of the TSOP382 (IR receiver) because otherwise, it will be too slow and not be able to decode any RC-5 packets.
To illustrate my issue, I have taken screenshots of traces on an oscilloscope and also drawn out my circuit. Please note that the center frequency was determined empirically and that the circuit is built on a breadboard. Originally I calculated I would need to use a 910-ohm resistor on T-Res, but ended up finding ~230-ohms produced the center frequency I require.
In the following image, the red trace is the 'signal' and the blue trace is the 'output'. As the screenshot shows, the LM567 takes 8ms before it reacts to the signal. When it finally does react, it oscillates for around 1ms before settling on a new output value.
To contrast this, I did the same experiment using the IR receiver (TSOP382) and the following screenshot shows the performance:
The IR receiver module takes less than 150uS to detect the presence of a 36kHz tone and it does not oscillate when it transitions. (Note: the input signal is 'ugly' because I am physically connecting the signal by hand - it does become 'clean' later in the trace)
These are some of my questions:
Thanks in advance!
- Justin
I am trying to build an IR receiver from the ground up using the RC-5 protocol. I am aware of components such as the TSOP382 (IR receiver) that does this all in a neat little package, however, I am trying to build a receiver from the ground up using a photodiode.
I have broken this problem into modules and I am using a tone-detector (LM567) to convert "the presence of a 36kHz tone" into a logic level. This is where I am having an issue. The tone-detector is incredibly slow to detect the tone and not only that, it goes through a period of oscillation before it settles after detecting the presence (or absence) of the tone.
To give some context, this is my first time working with a tone decoder, so I'm not sure if I have made a bad circuit or if tone decoders are actually this slow. Ideally, I want to match or come close to matching the performance of the TSOP382 (IR receiver) because otherwise, it will be too slow and not be able to decode any RC-5 packets.
To illustrate my issue, I have taken screenshots of traces on an oscilloscope and also drawn out my circuit. Please note that the center frequency was determined empirically and that the circuit is built on a breadboard. Originally I calculated I would need to use a 910-ohm resistor on T-Res, but ended up finding ~230-ohms produced the center frequency I require.
In the following image, the red trace is the 'signal' and the blue trace is the 'output'. As the screenshot shows, the LM567 takes 8ms before it reacts to the signal. When it finally does react, it oscillates for around 1ms before settling on a new output value.
To contrast this, I did the same experiment using the IR receiver (TSOP382) and the following screenshot shows the performance:
The IR receiver module takes less than 150uS to detect the presence of a 36kHz tone and it does not oscillate when it transitions. (Note: the input signal is 'ugly' because I am physically connecting the signal by hand - it does become 'clean' later in the trace)
These are some of my questions:
- Am I expecting too much performance from a tone decoder or is my circuit design unstable and causing the slow response? (perhaps due to using a breadboard)
- If I am expecting too much performance:
- What are some of the other options to explore? (Faster tone-detectors? Other IC's to do this job?)
- What kind of performance is to be expected?
Thanks in advance!
- Justin