The input gate of the HT12E is pulled high by an internal resistor (or an equivalent thereof).
Thus your signal source has to be capable of *sinking* current (ie pulling the input low) rather than *sourcing* current (ie pulling the input high).
I expect that your signal generator is only capable of acting as a signal source and cannot actively pull the output low. Stick a one transistor common emitter buffer after it, or equivalent, and I suspect that all will be well.
If you are talking about the "motor output" ports, these use L293D which are current sink devices and will handle up to an amp. Should be fine.
If you are thinking of using the piezo or IR outputs direct from the microcontroller chip - no way would I use those without buffering.
The IR output on J7 is capable of sinking several hundred mA and should be ideal though.
In both the above cases, I would suggest connecting via, say, a 47ohm resistor whilst you are still prototyping. Then, if you do inadvertently get a wire crossed, the sink current will be limited to within the safe limits of the output devices. The resistor shouldn't affect the normal operation at the bit rate you have.
Sue
Dear All,
I am building up a radio transmission link with 4 bits digital input signal(around 50-100Hz). I have got two RF modules which are 315Mhz radio transmitter and recevicer in 8kbps data rate. Also HT12E(encoder) and HT12D (decoder) have been used as well.
The circuit is working by inputting a 5V/0V (connect to 5V with switches) and outputting with LEDs. However, when I connected the input to the signal generator (input 10-100Hz square wave signal with 4.5V amplitude) and dectected the ouput with CRO, it doesn't work. Nothing can be outputted by the CRO. I am trying to send one bit as testing.
Please kindly help me to solve the problem. Do I connect it in a wrong way or is there any problem in the design? Thanks for your help.
Regards, Lok
Thanks Sue. So, do you think this circuit will work fine if I directly input a digital signal (not from signal generator but from HandyBoard "68HC11 microcontroller") into it?
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