UM28-CTH - Camera Telescope and Heater Controller

This unit was planned after I found myself on a timelapse trip where I needed to power a camera beyond the life of a standard camera battery and I wasn't using the UM12 motion control unit. The UM12 motion control rig has a converter to power the cameras but I didn't have a separate unit. I ending up having to drag the dolly out and simply use it to supply the 8v to the camera. A little cumbersome.

So I started out with a plan for a unit which could supply the needed conversion from the UM19 24vdc sealed lead acid battery unit to the 8v dc the Canon camera(s) needed. Then I thought "well while you're making a unit to power the camera why don't you include the other elements that you are likely to need in this situation. "

When I do timelapse during the day I tend to use the standard camera batteries if they are charged and available along with a intervalometer that runs off 2 AA batteries. So I thought why not put a small microprocessor in along with a small OLED display and arrange this to be an intervalometer for the camera. That would get rid of the need for extra non-rechargable batteries and the intervalometer unit. So I've added my shutter control output circuit from the UM12 motiona control unit which is a stereo 6.5mm output jack.

While on the intervalometer subject I do have Magic Lantern firmware on a chip for my Canon 5D mark 2 which I have mainly used to do Raw video but on the last trip I thought I'd give the inbuilt intervalometer a go and it failed several times so I am not willing to take the risk in future.

When doing winter night time star timelapse I would often, if not always, use a heater strap to keep the lens clear of dew. So I'll place a heater controller into the unit. But while thinking about this unit I realised I had another similar unit down my list which is for my telescope. I do astrophotography with my telescopes. So this also needs to have heaters on it so the decision was to have two heater element outlets. Easy !

Before I started designing the schematic for this unit I was reminded of the ULN2803A darlington chip. This chip has 8 darlington transistor pairs which are rated at 500mA each. This would make the unit quite compact over discrete transistors being used. So with this in mind I thought about what else could be controlled by this unit. Firstly, there is the reticle for my telescope. This is an eyepiece that is used for the alignment of stars when doing tracking. It has a target on it lit by a small red led. The ability to control the intensity led will help when faced with different intensity target stars.  I'll add an output for this. The other controllable item that I thought of was for the red lighting unit I have had kicking around that I could use to light my telescope work area. Astronomers use red lights for low level lighting as it doesn't affect their night vision adaption. This could be used for any sort of led lighting really.

To make the units heater outputs more flexible I have made four 1A outputs from the ULN2803A. Simply putting two of the darlington pairs in parallel, doubles their current handling.

A final output would be the 12vdc to power the german equatorial mount of the telescope. This will simply be a 12vdc buck converter. This UM28 unit will be powered from a 3 pin 24vdc supply and not 12vdc like the other units as I see this setup as independent from the UM12 motion control rig. I can't imagine using both at the same time. Though - famous last words....

UM28-CTH - Camera, Telescope and Heater Controller
As far as the software goes for the controller it would be similar in function to the UM27 lighting units. Again we have a rotary encoder with switch along with an OLED display. The display shows the values for each of the controlled outputs and the switch on the rotary encoder changes between the settings of these outputs. The display is momentary based on the rotary encoder being moved. A nice touch would be a red filter as one downside of these displays is they have no intensity control. Alas the red filter ended up being red texta !