Using logic level transistors as remote switches for programmatic inputs?

[student_moses]

Hello,

I was planning on building my DNA 200 box mod with an onboard Arduino Nano to handle addressable RGB LED lighting, tilt/accelerometer inputs, and capacitive touch inputs (mainly to sense when the user's lips are touching the drip tip).

In order for capacitive and tilt sensing to work properly, I need a way of using the 5v PWM pins on the Arduino Nano to register simulated button presses on the DNA 200. This is where a logic level transistor might come in. My plan was to connect the drain and source of a transistor to the Fire+ and Fire- pins respectively, and then connect a PWM pin to the transistor's gate and connect the source to the DNA's ground. This would be repeated for the Up and Down pins on the DNA 200. 

In theory, that would allow me to use the Arduino Nano to fire and adjust settings on the DNA 200, as the transistors should behave as switches. However, because I don't know how the inputs are designed, I can't say for sure. I've been operating under the assumption that the Up/Down + pins are just Vouts at the logic voltage of the board, and the - pins are sensing for voltage (indicating a closed circuit).

I was hoping that someone here could tell me if my assumptions about the operation of the DNA 200 are correct, and more importantly, if my idea of using transistors as remote buttons would work. I could just test it when my DNA 200 arrives, but I'd rather not fry it if I'm wrong.

Edit: fixed a mistake in my description of the wiring.

[student_moses]

Here's a diagram of what I'm talking about:
 
Q1 could be any logic level (threshold voltage < 5V) MOSFET.
S1 is just a momentary switch for manual operation.

[Tjroehr]

I fully believe this will work. Btw, wow that is the most creative idea I have seen in a while.

[John]

That will work on the up and down buttons. Fire is trickier, because it is active high, and at battery voltage. You'd need a P channel mosfet and a level shifter. 

But yeah, there's no reason you can have them driven by an arduino. 

On the other hand, if you used something with host USB port like a raspberry pi, you could drive it over the USB port.

[student_moses]

Thanks for the reply John. If I used a P-channel MOSFET in place of an N-channel one, and a level shifter to bring the output voltage of the Arduino above the battery voltage, wouldn't that just cause the MOSFET to turn off when voltage is applied? I'm not sure I follow. 

I'm also not sure why the fire pins being active high changes anything. Aren't the up and down pins active high as well?

[John]

No, they're active low. 

It wouldn't change anything if you were driving the gate of an N channel Mosfet located across the fire button pins with 17 volts, but most arduinos don't have a 17 volt output. 

The source of your mosfet will be at battery voltage. Turning an N channel mosfet on requires the gate to be something like 5 volts higher, which is why you'd need 17 volts. 

But you can do it with a P channel FET

[blueridgedog]

A question from a theory perspective:  Given that you will have a fully programable board in the enclosure (like the nano), wouldn't a USB interface and direct control be the way to go?  

[John]

I don't think the arduino nano has host USB. 

[student_moses]

As John said, the Arduino Nano doesn't have host USB, so I would have to use a host USB shield. If I find a 5V one that could reasonably fit in a box mod, sending commands over USB would be a viable option. 

Rather than use a MOSFET for the fire pins, I think I'll just opt for a small signal relay. There are some extremely compact ones available (this one, for instance), and the dimensions of any MOSFET circuit I made would likely end up being larger than the 19.3mm x 7.6mm x 5mm package specified for that model anyways. I'll just have to position it away from the magnetic latches.

[John]

A small relay would work swimmingly. 

[student_moses]

Well, it looks like a USB interface may be a viable option after all! I just found this host USB shield with dimensions of 25mm x 19mm, and it appears to have an option for built-in CDC protocol software. I might try to make that work as well.

[scoopy]

@student_moses you should check out the CloudMaker Ares chip....www.cloudmakertech.com There basing it on a lot of your ideas and are supporting community input and ideas in there development....although I'd love to have those type of options on a DNA 200 for sure

[blueridgedog]

They have yet to start to git repository for the project.  Unless I have missed it.  If you know where the community entry point is to this project, let me know.  As is, I have only had to assume that they have not started it.

[shinya]

student_moses said:

Hello,

I was planning on building my DNA 200 box mod with an onboard Arduino Nano to handle addressable RGB LED lighting, tilt/accelerometer inputs, and capacitive touch inputs (mainly to sense when the user's lips are touching the drip tip).

In order for capacitive and tilt sensing to work properly, I need a way of using the 5v PWM pins on the Arduino Nano to register simulated button presses on the DNA 200. This is where a logic level transistor might come in. My plan was to connect the drain and source of a transistor to the Fire+ and Fire- pins respectively, and then connect a PWM pin to the transistor's gate and connect the source to the DNA's ground. This would be repeated for the Up and Down pins on the DNA 200. 

In theory, that would allow me to use the Arduino Nano to fire and adjust settings on the DNA 200, as the transistors should behave as switches. However, because I don't know how the inputs are designed, I can't say for sure. I've been operating under the assumption that the Up/Down + pins are just Vouts at the logic voltage of the board, and the - pins are sensing for voltage (indicating a closed circuit).

I was hoping that someone here could tell me if my assumptions about the operation of the DNA 200 are correct, and more importantly, if my idea of using transistors as remote buttons would work. I could just test it when my DNA 200 arrives, but I'd rather not fry it if I'm wrong.

Edit: fixed a mistake in my description of the wiring.

[Gm111]

student_moses said:

Well, it looks like a USB interface may be a viable option after all! I just found this host USB shield with dimensions of 25mm x 19mm, and it appears to have an option for built-in CDC protocol software. I might try to make that work as well.

Will you please take a look at this video and would this work for Neil? https://m.youtube.com/watch?v=ceW0MEK-Z4w

[VapingBad]

Gm111 said:

[QUOTE=student_moses]Well, it looks like a USB interface may be a viable option after all! I just found this host USB shield with dimensions of 25mm x 19mm, and it appears to have an option for built-in CDC protocol software. I might try to make that work as well.

Will you please take a look at this video and would this work for Neil? https://m.youtube.com/watch?v=ceW0MEK-Z4w[/QUOTE]
Yep could just rip the air switch out of a cigalike auto battery and wire it to a DNA or many other boards, not investigated these switches but at worst it would need a simple circuit to support it.