How To Make Electronic Displays With Mood Ring Ink

Soychemist writes "Print some thermochromic ink onto a sheet of paper, put metal heating elements on the other side, and you have a rudimentary color-changing display. Chemists in the Whitesides Group at Harvard think that the devices could be used to provide a simple readout from cheap medical tests and kits that check water for pollutants. In the past year, the same scientists have made a three-cent medical test and improvised a centrifuge with an egg beater. Their aim is to invent useful gizmos with everyday materials."

Comments

Resistive ink

[Rorschach1]

I was thinking about making a thermochromic display for a custom watch, actually. Didn't know if anyone else had tried it before, but I guess I'm on the right track. It's going to take a lot of batteries to power, but I only really want it to run for Burning Man and Maker Faire.

I'm going to see if I can screen print resistive ink onto a PCB to make the heating elements. Failing that, I'll just go with thin film SMT resistors. Anyone know if that has been done before?

Re:Resistive ink

[Anonymous Coward]

I don't know if it's been done before, but SMT resistors will work quite well. Just make sure they're rated at the temperature the thermochromic ink needs to get to... if not, you could just solder some nichrome wire across the pads. You might want to consider heat sinking things so that it will be able to cool off quickly as well... a bit of a balancing act, that.

Good luck making it cool in time to wear while the man burns!

Re:Resistive ink

[Rorschach1]

Most of the films are rated for temperatures close to room temperature, though you can get other ranges. I've used through-hole resistors as heating elements before and they do indeed work quite well. A 1-watt metal film resistor will generate enough heat at 3 watts to melt its own solder joints. Long before that happens, it gets hot enough to melt through nylon or spectra, which is what I was using it for - a thermal knife for a load release.

It's certainly not going to be done in time this year, but maybe next. What actually inspired me was upgrading my desktop CNC milling machine's spindle motor so that it can handle cutting brass easily. I cut a few test shapes and I love it - it machines easily and looks beautiful.

I'm not really into steampunk, but I love some of the design elements. I'm working on a costume for next year that's sort of golden age of science fiction inspired, somewhere between Battlestar Galactica and a WWII German officer's uniform. I love the idea of a slightly bulky, machined brass wristwatch on a big leather band that's obviously electronic but clearly not a display technology in common real-world use, and I think it'll go well with the outfit.

Re:How is this electronic?

[__aajfby9338]

Seriously, there's nothing electronic about this, it's only the mood ring ink connected to a resistance. I mean, it's all right for a home experiment but it's hardly useful.

It's not electronic in much the same way that thermal printers aren't electronic.

Re:How is this electronic?

[Brett Buck]

Uh, it has to be "electronic" to be useful? Every hear of electric light? Or a toaster?

      Brett

Two questions

[raktul]

What temperatures are needed to change the ink? Obviously if it needs to be really hot that is bad since it might burn the person holding it, while cooler temperatures can be affected by the atmosphere around the page causing problems. Would it make more sense to use a different material then paper to print the ink on to avoid accidental colour changes?

The real article behind this

[wrmrxxx]

The summary links to Wired, which in turn links to the real article with the interesting details: http://www.rsc.org/delivery/_ArticleLinking/DisplayHTMLArticleforfree.cfm?JournalCode=LC&Year=2009&ManuscriptID=b905832j&Iss=Advance_Article