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The VT pin on the decoder side (signifying a valid transmission) flashes intermittently (sort of imitating a square wave pulse)

This happens without me making any change in the circuit - no address change, or TE' (transmission enable, which I have permanently grounded).

I put together a circuit that follows the schematic:

Transmitter schematic

(Source: https://electrosome.com/wp-content/uploads/2013/06/ASK-RF-Transmitter-600x823.jpg)

on the encoder side and

Receiver schematic

(Source: https://electrosome.com/wp-content/uploads/2013/06/ASK-RF-Receiver-600x557.jpg)

on the decoder side.

I'm using a Hi-Waote 6f22M battery power source, in case it is important.

Any reason you guys could suggest as to why it's not permanently high on the VT pin?

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  • \$\begingroup\$ Are you convinced that you have the oscillator resistors set correctly so that transmit and receive chips are compatible? \$\endgroup\$
    – Andy aka
    Jun 21, 2016 at 17:44
  • \$\begingroup\$ I would hope so, because while the circuit is in motion it shows that for a sizable amount of time that a valid transmission took place. But yes, I have checked with a multimeter, and resistances are within ~7 ohms of the given values, even the 1.1M ohm resistance \$\endgroup\$
    – Abhilash Dhar
    Jun 21, 2016 at 17:47
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    \$\begingroup\$ I find it odd that I see no bypass capacitors anywhere. Did you omit them for clarity of the image? I cannot imagine any circuit being stable without them. \$\endgroup\$
    – user105652
    Jun 21, 2016 at 17:52
  • \$\begingroup\$ No, I actually haven't added bypass capacitors in the implementation. Is there any source of AC noise that I could be missing, considering that I'm using a DC battery, and not an AC to DC adapter? \$\endgroup\$
    – Abhilash Dhar
    Jun 21, 2016 at 17:56
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    \$\begingroup\$ Neither the HT12E and HT12D show local decoupling capacitors, but they are very common. Place a 0.1µF ceramic cap directly across all IC power and ground pins, as close as possible to the IC's. \$\endgroup\$
    – rdtsc
    Jun 21, 2016 at 19:53

1 Answer 1

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I don't know what exactly caused the flashing part, but I know what resolved it - replacing the battery by a DC adapter, which made it work seamlessly. Thinking that it might have been because the battery wasn't "keeping up" with the demand, I tried to check if the battery was near it's end, and it was. But if it was slowly fading away, the intensity should have gradually reduced, so that still remains an unsolved question.

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