DIY Jobo

Hi.

I've been looking around for a while to see how photographers have made their home made Jobo. My goal is to keep my water temperature "tight" enough to process C-41 (+/- 0,5°C for the developper).

For this, many people are using the STC-1000 temp controller. Others use a PID controller (with Hysteresis control). For heating, I was thinking of using a portable water heater and a water pump to get even temperature.

My questions...

1. If I use a PID controller, which model should I buy? I was thinking of this model since it gives you the possibility to control the hysteresis.

2. Could a "good old" dimmer do the job and maintain the water bassin at 38°C +/- 0,5°C?

Thanks!

Look for a phototherm tempering bath unit - they were made for this, and should be tight enough for C41. They are on ebay from time to time.

For temperature control, I have a bias towards Omega or Watlow, they are reasonably priced but high quality.

Dear Draveur,

I built a Jobo work alike when I panicked and assumed that Jobo parts would no longer be available. At the time I had an old PID controller in the junk box but when it failed I purchased one similar to the one in your link. My suggestion, if you are going to continue your quest, is to look for one like this that includes a solid state relay. For circulation I use an aquarium pump something like this one and for heat I use an aquarium heater like one of these. I had to remove the temperature control board from the heater to get above 98°F.

Now for my real advice. If all you really want to do is process C-41 film in a normal tank just fill a plastic storage bin with warm water and process when the temperature is appropriate. After the developer, time and temperature are less important. If you really plan on building a drive as well, consider just saving for a nice used CPE2. Now that parts are available I wish that's what I had done. A temperature control system is the easy part. The mechanical drive system and water tank took me many more hours to build.

Good luck,

Neal Wydra

Please forgive my ignorance on this matter however perhaps my silly questions may lead to some insights for Draveur.
I have had idle thoughts about building a film processing system controlled by an Arduino (and many support electronics) in the past. My understanding is you would be able to attach a thermocouple or thermistor to the processor to allow for rather tight temp control.
I admit programming this would be very complex (for me at least) however my understanding is you may be able to calibrate the system to read ambient air temp and the current water temp and throttle a heater to maintain the desired temp, assuming you have a moderately well insulated tank or a large volume of water.
Would such a system be feasible? is the reason I have not seen something like this simply cost and complexity of programming.
Thank you for any replies in this matter.

Using one or two of these http://www.adafruit.com/products/381 with an Arduino or Raspberry PI would give you temperature monitoring. Then you need a heater and pump. Possibly a water level monitor if you are running at higher temperatures. Depending on where you are, you might need a supply of really cold water as well. Temperature controlled baths have been discussed here before.

Adding in motorized rotary processing, and things get complicated. That's why Jobos are popular. An ex-colleague of mine actually designed (and patented in the UK) a rotary auto fill/drain processor. It never saw production, but was very innovative. But it was years in development.

One has to be motivated to tinker in this area. I only have a little spare time, and my photography really needs it!

Thanks for your input.

DIY is half the fun and with a good dose of "brain juice", I believe that I can make something great for much less than the machines found on ebay and alike.

My goal is only the water bath (not so good thread title after all... sorry!). For the PID, I will take a look at Omega or Watlow. Thanks.

The question : is the auto-tuning of the PID good enough to maintain the water T°C? Or do you have to "fiddle" with the hysteresis (that I still dont really understand)?

Of course, a water pump for keeping the T°C even and a SSR. Does the relay need a heat sink?

For heating, I'm not shure yet of what to use, but it wont be a solution requiring device modifications.

I have thought using a Raspberry, but I think it would be "overdesign" for a waterbath (and I dont code).

For the curious ones : this is a good source of inspiration : http://vwblvd.com/?p=1563

Hysteresis is much the same as the slack in a mechanical gear system. You can calibrate going one way (with everything 'tight'), but there is an offset moving the other way. Heating and cooling systems are more involved, because turning off the heater does not make it temperature neutral immediately, and with a water bath there is the potential for uneven temperature. Plus there is a time delay while the water at the temperature sensor reaches equilibrium.