Converting normally logic 1 to normally logic 0 for momentary operation

[bluecar5556]

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?

 

[MikeMl]

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.

 

[bluecar5556]

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

 

[MikeMl]

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

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...

 

[bluecar5556]

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.

 

[MikeMl]

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.

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.

 

[bluecar5556]

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!

 

[bluecar5556]

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.

 

[bluecar5556]

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