Converting normally logic 1 to normally logic 0 for momentary operation

Hi, this is my first time posting on here and I just wanted to say that i'm not just looking for the solution as I am still learning what the heck I am attempting to accomplish here. Having said that I just recently purchased a Holtek HT12A/HT12D encoder decoder so I can remote control 4 momentary switches on a device. Each of the 4 switches (noted in BLUE on the receiver schematic) on the device I am attempting to control has one GND wire and the SIGNAL wire has an internal pull-up resistor at 5V. The mode of operation of the device I want to control has 4 momentary switches 5V at rest and when you press a button, it pulls the 5V down to ground via the other gnd wire and when released, returns back to 5V. Simple enough so I bought a 4 channel infrared remote control module and here is a schematic for the transmitter and receiver.

Receiver - **broken link removed**
Transmitter - **broken link removed**

I used a dremel cut off wheel to remove the entire relay portion of the receiver PCB as they will not be used and saves space inside the device. The data pins D8-D11 are normally logic 1 (5V) but when a button is momentarily pressed the corresponding data pin is logic 0 (0v) then resumes back to logic 1 (5V) as the button is released. How do I tie the switch 5v signal wire to the other switch gnd momentarily then resume back to 5 volts?

What is the value of the pull-up resistor to +5V on the Signal wires? The data r+eceiver likely has a very whimpy ability to sink current, and may not be able to overcome the current being sourced by the pull-up resistor. You may have to use rewire the transistors to use them as an emitter follower.

The application is a Volcano Vaporizer DIGIT with the Atmel ATMEGA16L-8AU microcontroller, I hope that helps...

bluecar5556 said:

The application is a Volcano Vaporizer DIGIT with the Atmel ATMEGA16L-8AU microcontroller, I hope that helps...

Click to expand...

Not a bit. You will have to look up the schematics.

Here is what I am trying to say about how you should connect the PNP transistors to interface with your external logic...

Oh okay, now I understand. The collector of the BC557 is GND so when D8 gets pulled low, the emitter is grounded from the collector? I hope i'm understanding this correctly.

bluecar5556 said:

Oh okay, now I understand. The collector of the BC557 is GND so when D8 gets pulled low, the emitter is grounded from the collector? I hope i'm understanding this correctly.

Click to expand...

Yes, the PNP is used as an emitter-follower. The emitter resistor is the pull-up inside your micro-controller board.


Uh Oh, you changed your request for the two transistor solution. I was working on it while you changed your request.

MikeMI you are AWESOME!! I will definitely use the 2 transistor solution as it most resembles the volcano's normal mode of operation and makes me feel better not sending a slightly higher voltage to a piece of equipment that has no schematics available for a good reason, so people don't copy a $500 device. Again thank you so much!

Just wanted to do a follow up and say that the circuit works flawlessly. I went ahead and put a 1k ohm resistor in series between the NPN transistor's collector and the microcontroller's signal wire. The volcano switch gnd is connected to gnd of the decoder's power supply.

To see the final product on youtube, go to
YouTube - What does a Volcano Vaporizer and NES controller have in common?