Do you mean burst of 1000 cycles, or about 25 ms at 38 kHz?
The 4013 changes state on a positive clock, or after about 13 ms (27k and 0.47 uF). The discharge time constant prevents retriggering for about 1/2 second (1 M and 0.47 uF). Do you want it to toggle faster than once per second? The danger is that you could get multiple pulses from a buttonpush (if that's what the input is coming from) and have the toggle end up in a random state.
Or you could add a pair of uProcs and trasnmit specific codes which would make it much more robust. I couln't get the Freescale 68HC908 series to modulate 38KHz directly - possibly a lack of programming skills on my part but with a little added glue logic it works fine. Receiving is not at all difficult. TV remotes (Samsung and Sony for certain) transmit 32 bits total with mirrored 8 bit blocks. It's pretty reliable. You can do it too if it's important.
No. Datasheets indicate that, for noise suppression, most IR receiver modules are optimised to receive 38kHz pulses in bursts roughly 0.5 msec on, 0.5msec off. This is where I derived the ~1kHz figure from.
I _am_ building something using an IR receiver module, but using another technique. It's just that I came across this circuit more than once and got curious about the validity of the design.
I get your point about unintentional toggles. Anyway, I tossed in the matter of filter time constant as an afterthought. My attention was mainly on why the designer(s) considered it necessary to use R3 and D1. The pulsed output from Q1's collector is already unidirectional and does not need rectification. The collector, even without a reverse blocking diode, is essentially an open circuit (megohms) in the off state and will have negligible effect on the filter efficiency.
Thanks for your interest. It's not that I want to build this design. I'm using a different approach in something I _am_ building. It's just that I came across this circuit and the inclusion of R3 and D1, while apparently logical at first, seems superfluous on closer inspection. Please also read my reply to John O'Flaherty.
The diode gives a different time constant for discharge than for charge. If the diode is shorted out, the 100 k collector resistor will shorten the discharge time constant to 0.13 sec or so, by paralleling the 1 Megohm. However, if you can get by with a 1 megohm collector resistor, based on the transistor leakage and the IR receiver turning the transistor fully off, it should work as you've drawn it.
BC5xx transistors have very low leakage - Ices 4uA max at Tj 150 C. Actual leakage encountered in practice are probably much less even at 150 C. And Tj in the target hobbyist use is unlikely to exceed 50 deg C. So we can expect sub-100 nA leakage.
I haven't seen leakage figures for the output of an IR receiver module. Anything less than 10uA will be shunted away by the 27k paralleling b-e and won't cause Q1 to conduct.
If I were to adapt this circuit for my own use, I'd probably use a higher capacitance for C1 (an electrolytic should be OK) and correspondingly lower values for R4 and R5. Say 2.2uF, 4.7k and
Block diagrams on manufacturers' datasheets usually give the output as the collector of an NPN BJT, like the output of popular comparators but with a 20-30K internal resistor to Vcc. This is probably meant to enable driving the base of an external NPN BJT without any external component.