Todd Welsh

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Todd Welsh

Computer Programmer (

Hobbies: Beekeeping, Tae Kwon Do instructor

08/10/2011 Project Idea - Automated Hot / Cold pack for minor injuries

Requirements in order of presidence: Safe, Effective, Affordable, Available, Programmable.

Basic description: A heating pad and a bag are sandwiched together to for the hot / cold pack to be placed on the body. There is also a cooler full of ice water with a tube connected from the bag to the cooler. A microcontroller will turn the heating pad on or off. It will also pump water from the bag to the cooler and vice-versa.

Need to avoid liability. This will probably be plans for a device to be built by someone, not a product.



Hot water bottle. They are used for cold too. (Other choices were IV bags and colostomy bags.)


Pretty much anything. Just run the tube under the lid with something rigid next to it so it does not get pinched.


Decided on 3/16" air tubing for fish tanks. I would like to only have one tube going to the bag and one to the cooler for simplicity.

Heating pad

Moist heat heating pad available at the drug store. It would be best to find one that does not use AC.


A pump that goes in one direction requires valves to reverse the direction of water like an h-bridge. A 2 direction pump might be more expensive but it will make things less complicated. Model airplane fueling pumps are under 20$ and are reversable. Uses 3/16 inch tubing. Is it too slow? Can I put the switch on forward and control the direction by reversing the polarity?

Other Thoughts: garden fountain pump - Doesn't work well in reverse, washing machine pump, windshield washer fluid pump


Solenoid valves are about 10$ apiece. I need 4 of them to reverse direction of water flow. Too Expensive


Arduino or a ATiny


Need GFI. Since this will be a combination of AC power and water. Can you get power strips that do that? Turns out you can

Straps Velcro / Elastic to hold pad on injury.

First Post

I am new to this making thing. If I need to solve a problem with software I can write it myself, download it or more likely modify downloaded code. If I need to solve a problem with hardware... I don't know where to begin. I read this online book: It does pretty well until you get to transistors.

I enjoyed the arduino class dry run. It was my first time soldering anything substantial. No (bad) burns. Once I got the hand of my soldering iron (It is a little slow to heat up) everything went great. I just need a few changes to be able to connect the arduino board to my power supply / board and I will be set.

To get started, I bought several "packs" from digikey and some others. A couple of solderless breadboards. I'm working my way through a power supply from here:

Next I would like to make an altoid tin soldering fume extractor:

From there I think I should be able to tackle this solder practice kit: and the learn to solder kit

I forsee a chicken-and-egg problem because the fume extractor requires soldering and I would like to have the fume extractor while I practice soldering....

Projects I am thinking about long term: 1) I want to make some kind of remote monitoring device for beehives where It would sms/tweet/blog/whatever the status of the hive. It would have to be solar power or low power/battery. For communication I would like to use a cheap old cellphone. There are several DIY projects on line that say how to do parts of this. It is just a matter of mashing them all together for my pupose. 2) An interface that would translate buttton presses from a game controller to keyboard buttons in the OS via USB. I'm trying to figure out a way to do it cheaply. (keyboard controller chips are more expensive than cheap keyboards!?!?.) Static electricity will be an issue.