Remote IR on-off switch

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.

--
John

399/irswitch.png

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.

G=B2

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.

[snip]

You are correct. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

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.

I see what you meant, now.

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.

--
John

Omitting the 100k resistor will obviate that.

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

220k respectively.

Right. I was addressing your question about the validity of the original design. I think they wanted the collector to switch to ground quickly and leave the discharge controlled by the 1 megohm.

I have no idea what the output circuit of that IR thing looks like, but as long as it reaches nearly to the positive rail, it should be fine.

Makes sense.

--
John

Nope. R3 isn't used in pimpom's version, as shown on the right side of...

...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

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.

--- Even better: (View in Courier)

+5 | +-----+-----------+ | | | | [10k] | | | E | +--[10k]--B PNP | | C [IRRX]---+ | | | +-----+---->4013 CLK | | | | | | [470nF] [1M] | | | | +-----+-----------+-----+ | GND

That way the cap would charge up very quickly and discharge slowly, making an excellent debouncer for the 4013's clock.

Also, I like the idea of driving the base into saturation through a single resistor pulled down to ground rather than through a voltage divider.

---

--- The circuit is most likely activated by a push-button controlled CW infrared transmitter, so there'd be no modulation, and no need for a filter other than that required to debounce the signal into the 4013's clock.

JF

--
Or a PNP with a single external resistor.

JF

CD4013 does not have a ST input on the clock, and that will violate the max clock rise/fall times. Would be okay with a HC14 or other ST gate before the clock input.

--
Yup, good catch.

Thanks. :-)

JF

Lets see, Diode to prevent the 100K from draining the REF down faster than the 1M that is there.

Resistor to remove the in rush currents on the pulse from the transistor? Which also may lead to parasitic abnormalities.

Just my guess.