Battery third (temp) terminal as multipurpose analogue input - page 11 - Hotwire! Hardware Mods, Accessories and Insights - CHDK Forum

Battery third (temp) terminal as multipurpose analogue input

  • 199 Replies
  • 80084 Views
Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #100 on: 24 / January / 2014, 09:48:55 »
Advertisements
Nope, did not copy that. Om about two hours I will have the first circuit ready I hope

*

Offline ahull

  • *****
  • 634
Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #101 on: 24 / January / 2014, 11:22:46 »
I think I may have spotted a potential problem, the A/D converter input must have some sort of pull up resistor (to +V (A/D Ref) presumably), the value of which we don't know. The Ixus 65 diagram doesn't show this resistor, so it is probably internal to the A/D converter.

We can guess however from here... http://chdk.setepontos.com/index.php?topic=10385.0 that this value is probably pretty high, so there may not be sufficient current flowing through the output section of the PhotoMOS to switch it on.. The photo sensor(s) in the output section rely presumably on a small current being available from the voltage being switched, in order to turn itself on, and thus switch on the main mosfet. If the pullup resistor has too high a value, we may never get enough current flowing to make the thing work.

I hope I am incorrect here, but it is worrying me slightly. There is little risk of damaging anything here, it just might not work as we expect.
« Last Edit: 24 / January / 2014, 11:28:48 by ahull »

Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #102 on: 24 / January / 2014, 11:31:39 »
I have limited experience with the using MOSFET's in this sort of circuit so have no idea about suitable biasing or threshold currents on the output side. 
I think I may have spotted a potential problem, the A/D converter input must have some sort of pull up resistor (to +V (A/D Ref) presumably), the value of which we don't know. The Ixus 65 diagram doesn't show this resistor, so it is probably internal to the A/D converter.
That's why I made my original comment.

If threshold current through the MOSFET is an issue,  we can alway add a (lower) pull up resistor in parallel with the one in the A/D converter.
Ported :   A1200    SD940   G10    Powershot N    G16

*

Offline ahull

  • *****
  • 634
Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #103 on: 24 / January / 2014, 11:47:50 »
Good point, since we have access to both power rails, I suppose it isn't a major issue.

I was also thinking about the best way to couple together all of the inputs to 50+ cameras. It might be possible to use a whole bunch of 1uf or so capacitors, all going to one photomos switch (since we are only really interested in sending a pulse). The disadvantage is that the pulse would have to be "seen" by polling the AD converter fairly frequently, so timing and a suitable value for the coupling capacitor would need to be worked out.

This would have the advantage of no DC path between the cameras, and only needing to toggle one pin to trigger all of the cameras, so synchronisation of multiple input pins is not necessary. This idea is no use however if we want to trigger them all at slightly different times. 

I don't know if perhaps I might be over thinking this.  :D
« Last Edit: 24 / January / 2014, 11:51:30 by ahull »


Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #104 on: 24 / January / 2014, 12:12:47 »
Cough cough! Sorry, can't follow that. Should I change anything? Still working on the first dummy.

Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #105 on: 24 / January / 2014, 12:22:23 »
Cough cough! Sorry, can't follow that. Should I change anything? Still working on the first dummy.
Keep going.
Ported :   A1200    SD940   G10    Powershot N    G16

*

Offline ahull

  • *****
  • 634
Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #106 on: 24 / January / 2014, 14:04:51 »
Cough cough! Sorry, can't follow that. Should I change anything? Still working on the first dummy.

Carry on, I'm just thinking out loud..  :D

Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #107 on: 24 / January / 2014, 18:34:37 »
Okay, now having the proof the circuit is working at least at small distance cables. I have patched it all at an Arduino breadboard shield where it works nicely. I feel good with the PhotoMos, somehow it is calming that the Arduino is connected to the camera only by light. :-)

However I failed to bring it all into the dummy, now I resign for today. I finished the dummy completely, but somehow it did not work. Same circuit and so on, but I must have an error somewhere. When measuring the dummy with the multimeter everything looked good. Now this was only the first approach, tomorrow I'll do the next one.

At least as a milestone on the way here is the proof the circuit works: (Not available before this posts time +45 minutes, because I don't have a Vimeo Pro account.) The Arduino just plays the "Blink" example at 6 seconds delay.

Once again thank you all very, very much for your help. I am now almost sure I will - with your help - make the project succeed. :xmas
« Last Edit: 24 / January / 2014, 18:42:10 by Karmaschinken »


Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #108 on: 25 / January / 2014, 17:43:00 »
Very good news from here. I got two dummies working and the sync times seem overwhelming good. Much better than every thing I ever had before. Although it's probably some more work than the usb switching solution I sm absolutely sure it's worth it.

Two cameras are taking pictures of the LED field, every LED lit for a second, and I have not seen a single image with differences yet.

I'll post the results as  series here later.

Once again thank you for all the helping ideas and work you did so far.

Re: Battery third (temp) terminal as multipurpose analogue input
« Reply #109 on: 25 / January / 2014, 17:45:12 »
Two cameras are taking pictures of the LED field, every LED lit for a second, and I have not seen a single image with differences yet.
Is this a typo ?  Every LED lit for a second?   I had assumed you would change your LED pattern every millisecond and look for differences?
Ported :   A1200    SD940   G10    Powershot N    G16

 

Related Topics


SimplePortal 2.3.6 © 2008-2014, SimplePortal