External 'safety' switch for board

[fostac]

     So I'm making a mod that needs to be able to prevent the DNA 200 from firing via an external microcontroller. My first thought is to tap into the six pin button breakout header on the left of the board and drive the buttons via the microcontroller similar to this. However, I believe I'll run into problems with the board unintentionally firing when entering locked-mode, stealth-mode, etc. even when the safety is supposed to be on. I'm looking for a way for the safety to only restrict firing of the coil without interfering with mode-switching or other commands.

     So then my thought is to interrupt the connection to the coil with something like a mosfet. That way I get the 'Check Atomizer' error when the board tries to fire unless the microcontroller controlling the mosfet lets current through. This is the method I want to use, but I can't there is a mosfet or relay small enough to fit in the case and be controlled by the microcontroller that also could handle the crazy output current.

     If you have any suggestions or if I'm missing something on the board, then I could really use some help

Thanks!

[Mad Scientist]

I understand what you're doing and I think it's a great idea. I have something similar in mind also.

What I plan to do is monitor the DNA output connection through an analog input on my processor (I use PIC chips but most processors these days have analog inputs).  On a PIC at least, the input impedance of an analog input is ~= 10 KOhm.  A voltage divider with that impedance to an analog input would allow the processor to "test" the DNA mode (like fire for a few mS -- as much as will get past the DNA debounce -- and see if the DNA output has a voltage consistent with "fire" on it) and determine if it was locked or not, and the high input impedance would not have any effect on the DNA resistance measurements.  This would prevent the processor from getting out of sync with the DNA for having all controls through the processor.  

One issue is the new coil up / down question which is a bit of a wild card and the software would have to be able to deal with that -- I haven't decided how to handle that yet.  That is a third "mode" that's not locked but not unlocked.  I guess the software could test to see if it can toggle between lock/unlock and if neither gets any fire voltage, then it's likely in new-coil-question mode (or maybe low battery or maybe shorted or . . . more testing needed).

Another advantage of PIC chips are their small size and cost and the ability to scale up if needed.  A 1K word eight pin processor with on chip A to D needs a few square mm of space and costs about 50 cents in reasonable quantities.  1K of program space is way more than enough to run the DNA controls.  The next increment would be 4K . . . up to hundreds of K.  They have midrange chips with USB so you can dispense with most of the button stuff (still need the FIRE button control).  If you want to get really crazy, they also have chips with integrated LCD control and capacitive touch inputs for a few dollars each -- the sky is the limit for the human interface.

[blueridgedog]

What would be the real world outcome of this pursuit?  What conditions would prevent the mod from firing where it currently would in an undesired way?  Currently I can either lock the device or remove the atomizer to achieve a no fire state.

[Mad Scientist]

blueridgedog said:

What would be the real world outcome of this pursuit?  What conditions would prevent the mod from firing where it currently would in an undesired way?  Currently I can either lock the device or remove the atomizer to achieve a no fire state.

I took the OP to mean a desire to control all functions including firing through a uP. I want a rotary encoder for temp setting as a first cut. Using a chip without USB interface and host stack means just pretending to be the buttons to the DNA200 switch header. Since that just seems really klugey the more I think about it, I started looking at the PIC 24FJ128. Ideally evolv would open source at least some of the software (like the UI hint hint) to link to a protected library but I won't hold my breath -- although that will likely happen before the whiteout open source is ever released lol.