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Remote Control Extender Mk2 Robert Clark's Modifications

I built your remote extender and it works GREAT. Thanks for the design!

FYI - I made two small changes - that drop the parts count of the REMOTE end, and improve the performance. I have a attached a scan of the MODIFIED CCT Diag FYI.

As you will recall....in MK-2 (and MK-1) you are sending one pulse for each flash of the infra-red as a negative current pulse from the REMOTE unit to the BASE unit.

On the REMOTE end, I used a ROHM RPM-7136 (http://www.rohm.com/products/shortform/27photo/1irda.html) IR Receiver AND Demodulator. This device is not much bigger than an LED....but includes the amplifier, and 38kHz Demodulator. The output of the RPM-7136 is normally HIGH, and goes LOW when a 38kHz IR is detected. I then used your existing line driver to drive the cable as before.....but the difference is that the pulse rate is MUCH lower than 38kHz. Not that this matters....but the simplification, size reduction, and parts count reduction on the remote end was the objective.

On the BASE end.....I had to re-modulate the signal onto a 38kHz Carrier. So.....I added a 555 timer, set to run at a fixed 38kHz (50/50 duty cycle mode)......and gated the 555 ON/OFF with the signal coming from the REMOTE. (OK....more complicated as I needed a scope (or freq counter) to adjust the 38kHz oscillator...and it could drift with temp/time.....and my mod means that this design will ONLY work with Remote Controllers that use a 38kHz carrier.....so I accept the argument that I have NOT improved the design overall.)

In case you can't read the image...the LM555 connections are...

Pin Connection
1 GND
2 (Shorted to pin 6) AND (to 1K5 resistor to 500R trimpot to pin 3)
3 (to 1K0 resistor to base of TR4) AND (to 1K5 resistor to 500R trimpot to pin 2)
4 To R11/TR5 junction
5 to 0.1uF cap to GND
6 (0.01 uF cap to GND) AND (shorted to pin 2)
7 No Connection
8 VDD

 

NB: approx 1800 ohm between pin3 and pin6 gives 38kHz

One more thing.......just realized the design I sent you might blow the NE555 chip. The unregulated supply might exceed the max Vdd for the NE555 (ie 16V).

To be honest ... I used an ex-mobile phone charger (12VDC, regulated) instead of the full-wave rectified (unregulated) supply in the orig cct.

I guess if a 7812 (12V regulator) was added to the cct...it would work fine.

Back to Remote Control Extender MK2 Diagrams


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