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I would like to wirelessly transmit 2 bits without a microcontroller (basically control 2 LEDs wirelessly...), as having several receiving nodes the cost of the project would be driven very high.

I thought of using cheap AM RF modules (such as the Quasar QAM-TX1 coupled to the QAM-RX2), then code the 2 bits on the frequency output of an astable 555 and count it on the other end, but the system gets quite complex, difficult to implement (I am currently struggling to a. get a frequency which is multiplied by 2, 4, 8 from 2 switches only).

Am I neglecting an easier option?

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  • \$\begingroup\$ Can you use infrared as your wireless link? \$\endgroup\$
    – HL-SDK
    Commented Oct 14, 2013 at 19:54
  • \$\begingroup\$ Thanks for the quick answer. No, I don't have line of sight. Why does it make a difference (the modules are supposed to mirror input/output)? Edit: Oh, right. A stable output is going to induce a lot of noise with RF... So no, can't do. \$\endgroup\$
    – Mister Mystère
    Commented Oct 14, 2013 at 19:55
  • \$\begingroup\$ Because an infrared implementation will be a few times less expensive. You can use pulse width modulation to send the 2 bits. On the receiving end you would time the pulse width and compare it to get the bits back. \$\endgroup\$
    – HL-SDK
    Commented Oct 14, 2013 at 20:00
  • \$\begingroup\$ I exactly did that for a recent project, but I used a microcontroller. I cannot think of a simple way to measure pulse widths with discrete ICs if I use that in conjunction with RF... What would you do without microcontrollers? \$\endgroup\$
    – Mister Mystère
    Commented Oct 14, 2013 at 20:02
  • \$\begingroup\$ Originally I was going to say a comparator feeding an integrator, but you should be able to get away with filtering the receiver digital output and feeding a window comparator. Effectively it turns the PWM into an analog voltage and the window comparator discretises it. \$\endgroup\$
    – HL-SDK
    Commented Oct 14, 2013 at 20:07

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Here's what the OP suggests and I've pointed out that you can buy a chip that directly interfaces with both ends that gives you 4 independant switches: -

QAM-TX1 in Farnell costs about £3.00 which means you can probably buy it for $3.00 elesewhere. The REF600E costs about £2.50 in Farnell and the same reasons as above will cost about $2.50: -

enter image description here

For the receiver the QAM-RX2 (as specified cost from Farnell £3.65 and so you can probably get it for $3.50. The RF600D is £3.12 from you know where and probably $3 elsewhere.

enter image description here

It's about as cheap and uncomplicated as it comes without a micro but maybe there are other options.

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  • \$\begingroup\$ Believe me or not but I had seen it in the datasheet and completely erased it from my memory somehow (at that time I still thought I could do easier and cheaper for 2 bits)... This is exactly what I wanted, thanks. Dividing the cost by nearly 4 per node is quite good; I could have used shift registers like the 74HC595 and 164 to halve it again but it isn't an integrated solution (e.g. need a clock on both ends). \$\endgroup\$
    – Mister Mystère
    Commented Oct 15, 2013 at 8:09
  • \$\begingroup\$ Coolio. Glad to help. \$\endgroup\$
    – Andy aka
    Commented Oct 15, 2013 at 8:13
  • \$\begingroup\$ @Andyaka HT12E and HT12D \$\endgroup\$
    – yogece
    Commented Oct 15, 2013 at 15:26

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