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Canon 1100D set-point cooling mod


Jokehoba

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I thought I would share with you last summer's project to add set-point cooling to my DSLR. It took about 3 months and wasn't actually required much over the cold winter months. I've made a few minor changes since the winter. The original white-on-blue display packed up so I replaced it with this black-on-green one. And the original ball-bearing fan introduced vibration when using my SCT (not apparent on my other scopes), so I've replaced it with a MagLev/vapo type. Unfortunately I haven't had any clear skies to test the new fan...

My main design criteria were:

  • Cold-finger/peltier cooling
  • As little 'destruction/deconstruction' of the camera as possible - I wanted it to still look like a DSLR
  • Achieve 5-10 C set-point cooling, as I felt this gave acceptable low noise
  • Include a dew heater/indicator for the front filter
  • Arduino controlled with display to provide useful feedback on settings and simple controls

I give due credit to Gina and Rowland Cheshire, having read their many inspirational posts on cooling (both here and on Ice in space) which helped me to hone my design.

Image with the camera shows fan-heatsink-peltier-bracket construction. The connection box is screwed to the tripod mounting. The white sensor measures ambient temperature and RH. The controller images show approaching the set-point and at set-point. A red LED above the main display lights up when the dew heater is active. The display shows:

  • Set = desired set-point temperature
  • CMOS = temperature of cold-finger close to sensor
  • Fltr = temperature of front filter
  • Dew = number of degrees above the dew point to maintain the dew heater
  • TEC = heatsink temperature (hot side of peltier)
  • PWM = percentage output sent to the peltier (I've limited it to 90% max)
  • Am = ambient temperature, DP= dew point, RH = relative humidity

At some point I will tidy the heatsink side to conceal the cables, etc.

John

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I'll dig it out. Must be on my other PC...

Found it!

The code was largely based on Njal Brekke's PID controller - https://ragnablade.myon.no/?page_id=84. There's some handy graphs of peltier performance too.

I've customised the sketch somewhat for the particular digital temperature sensors I've used and the larger display, and the added dew-heater circuit. But otherwise this was my starting point.

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fairly standard stuff :) 

being a full time geek (and programmer) i'm trying to figure out using AVR and timer interupts to make the code run more responsively... 

good nerdy reading http://www.engblaze.com/microcontroller-tutorial-avr-and-arduino-timer-interrupts/:D

also, trying to get my head around eaglecad as a custom circuitboard seems like fun. not made a PCB for years so am just a tad rusty...

 

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10 hours ago, Dave_D said:

fairly standard stuff :) 

Agreed, but having not written any code for 10 years or so, I needed a starting point. Final code runs to double the length!

The rotary encoder code uses timers and interrupts to monitor button presses and turn of the control. I opted for readily available libraries for this. At the time clear skies were coming and going, and my camera was in bits... Perhaps I should post some explanation as to how it all works?

I looked at EagleCAD, TinyCAD, QUCS, and ngspice. In the end I found RS Components DesignSparkPCB to be an excellent (free) design tool - simple and intuitive. For the breadboard layout I dabbled with Fritzing and VirtualBreadboard. 

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just had a look at designspark, looks good and probably does everything i'm looking for. just hope it has my component list... finding my schmitt triggers (going with hardware debouncing)  in eaglecad gave me a headache lol

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