K-12 Engineering: Squishy Circuits Tips and Tricks

[Update, June 6, 2012: Want to try making play-doh circuits at home?  Read the Squishy Circuits official site first!]

A caterpillar named Earl

I don’t remember who pointed me to this TED talk about making working circuits with play-dough, but I found the idea compelling.  When a local Brownie troop called my school and asked if the girls could visit the campus to learn about one of our trades programs, it seemed like a good fit for this activity. I figured I had found an opportunity to do something fun and expose some kids to what’s available at a trades/tech school.  I didn’t anticipate that by the end of the evening, 20 kids would be jumping up and down with excitement, proclaiming the incredible coolness of building electronics, refusing to be torn from their creations until they could be demonstrated to volunteers and parents, and vowing to go home and take apart their vacuum cleaners.

Last Tuesday evening, twenty or so girls between 5 and 8 years old arrived at the campus.  The “squishy circuits,” as developers from University of St. Thomas call them, were a huge hit.  Compared to other electronic projects such as soldering kits or robot-building, this was by comparison inexpensive, easy to set up, and required relatively little technical expertise from the volunteers.  Here’s what we did.

Two weeks ahead

Recruited some volunteers.  We had one adult for every four kids: some were students in my program, others were Brownie leaders who may or may not have had any background with electricity.  Volunteers did things like encourage kids, take pictures, fetch extra supplies, make sure no one got hurt, and occasionally make suggestions of things to try when someone got stuck. We probably could have gotten away with half the number of adults.  But I found that the kids really wanted to show us their triumphs — it helped to have a surfeit of “witnesses,” as well as several cameras.

Assembled supplies.  For electronic supplies, we ordered from Digikey — they have reasonable prices and they ship overnight.  For craft supplies, we hit the dollar store.

The trickiest thing was to find safety glasses that won’t fall off the kids’ faces.  An LED can explode into tiny bits of plastic shrapnel if connected directly to a 9V battery, so safety glasses are definitely necessary. I visited a local industrial-supply store and bought a model designed for women.  They sold them to me in boxes of 10, and they fit the kids fine. UST has suggestions about what to buy and where to find it, including inexpensive mail-order safety glasses in kids’ sizes.

One week ahead

Dough starts liquid, then clumps like ruined gravy, and finally stiffens into a ball

Made the dough.  Recipes are here.  I planned one batch of conductive dough and half a batch of insulating dough for every three kids, which was a generous amount.  I used a teaspoon of grocery-store-grade food colouring for every batch.  The recipe can be multiplied, but it’s very stiff to stir at the end.  I was stirring by hand, and a double batch was the most I was physically able to work with.  The dough keeps well for over a week if kept at room temperature in a sealed plastic bag.

Gave the volunteers a chance to experiment with the dough, and briefed them about how the workshop would go.

Crimped terminal lugs onto the ends of anything with wires.  The helpful folks at UST say that it’s recommended, not required.  We didn’t have time to add lugs onto everything, and circuits work without them.  But we found that kids who had terminal lugs were able to bring their imagined creations to life, such as Earl the caterpillar, above; kids who didn’t have terminal lugs were able to make lights and buzzers turn on, but got frustrated trying to make it look like the butterfly, elephant, or “spider-cat” they imagined, because the wires kept slipping out of the dough.  UST also recommends soldering the lugs; I’m not sure that’s a big advantage, and it significantly increases the skill needed to prepare.  I used fork lugs (sometimes called spade lugs or Sta-kons); if you can find the type with a hooked end, it’ll work even better for grabbing on to the dough. The lugs and the tool for attaching (aka crimping) them are available from the automotive section of a hardware store.

Day Of

Figured out seating and logistics.  We had tables of four: three kids and an adult.  I didn’t want the supplies on the table when we started, because I needed the undivided attention of the kids while I talked about safety, so I made a bag of supplies for each table but left them at the side of the room: one motor, two batteries, one buzzer, a handful of popsicle sticks, one batch of conductive dough, half a batch of insulating dough, etc.

Workshop Agenda

As people were arriving, they took a seat at a table that had pencils, markers, nametags, and blank paper.  We encouraged them to draw the animal (real or imagined) that they would like to make tonight.

This is me, doing the initial demo

15 min: When everyone was seated, I introduced myself and introduced the play-dough.  I asked everyone to put on their safety glasses.  I demo’ed three circuits: an LED circuit in conductive dough (which I showed with the LED in forward and reverse bias), an LED circuit in non-conductive dough, and a short circuit with an LED.  We had a brief conversation about the idea that “electricity has to go through things” in order to make them work.

Safety briefing: there are two rules.

  1. Batteries must always be connected to dough, not directly to other components.
  2. Wear your safety glasses.

15 min: First mission: figure out how the components work.  I showed them the buzzer, button, and motor, and asked them to hook them up to test them.

45 min: Once kids were getting confident about making lights light up and buzzers buzz, I got their attention and asked them what they wanted to build.  Was it an animal whose eyes lit up, or a monster that made noise when you pressed a button?  I solicited ideas from each table, mostly so that any kids who were at a loss about what was possible could hear a few different ideas.  Then I let them go at it, and circulated with the volunteers.

15 min: When the evening was almost over, we brought the kids together and walked to the electronics shop, where we demonstrated some considerably larger lights and motors, and talked a bit about what it means to do this for a living.  Many of them had questions about motors (like in ceiling fans and vacuum cleaners) as well as sensors (like in the drinking fountains we had passed or in auto-flushing toilets), so we talked about that for a bit.

I didn’t really have a good way to end the workshop.  I would have liked to spend a little time having them think about what they noticed, or what they might like to build next, but couldn’t really clear up in my head what I was aiming for.  So, I thanked them and told them they could take their creations home (except for batteries and motors).  We headed back to the activity room, where many of the kids would have happily gone back to making stuff if the arrival of their parents hadn’t interfered.

Total workshop time: 1h 30 min.


The room was, predictably, a wreck.  We spent an hour wiping dough off of tables, sweeping it off the floor, etc.  Any component that had been in the salt dough had its leads corroded beyond use.  The instructions from UST suggest wiping down the component leads with fresh water, which might have been worth it if we had any components that weren’t hideously disfigured.  Instead, we just clipped all the terminal lugs off.  We’ll crimp new ones on next time.

The other thing I would do next time is get cheap picnic tablecloths from the dollar store, to help contain the mess.

How kids were thinking about electricity

Many kids figured out that any place you connected one LED, you could connect a second one (a parallel circuit).  But most had trouble imagining a circuit with more than 2 nodes (a series circuit), and consequently had trouble making their designs a reality.  It made me wonder if I should demonstrate both ideas at the beginning.

Consequently, we had a number of kids using the pushbuttons to short out a light.  This worked fine and is not dangerous, as long as the battery terminals are connected to dough: the conductive dough has about 10KOhms of resistance in a finger-sized piece.

Many kids had trouble distinguishing the pushbutton from the devices it was supposed to control.  For example, one girl wanted her circuit to make noise, and was frustrated that it wasn’t working.  She had wired a button into the circuit — apparently visualizing the button itself as the buzzer.  It made me wonder if next time, I might not hand out the buttons until the kids had explored the other components.

One student discovered that even the non-conductive dough would allow an LED to light up, if you didn’t use very much of it.  She was very excited about this and came over to let me know that I had been mistaken… which naturally I was also very excited about.

Notes for next time

For making creatures or other representational art, it works best to connect and test all the active elements first, then embed them in conductive dough.  For example, to make a pig with glowing eyes and a rotating tail, connect a battery, 2 LEDs, and a motor.  Once they are all working, build the pig around them.

Many of the kids were talking about wanting to continue to experiment at home.  I wish I had had some kind of handout or recipe card with more information about electronics for kids, and links like the ones below.

I had two batteries for each table of 3-4 kids.  Some kids clearly preferred working together, but others didn’t.  In retrospect, it would have been better to have a battery for each child.

Where to Buy

UST has lists of parts available from Radio Shack / The Source / Circuit City (name varies by location, it’s all the same store).

You can also get reasonable prices for small quantities by mail order from Newark or Digikey; I find their websites easier to navigate than some other online retailers.

Finally, there’s the Squishy Circuits Store.  They sell a kit of components appropriate for one child.  More expensive than ordering in bulk from a distributor, but more convenient too — especially if you’re not familiar enough with the components to know what to buy.

Supply list

  • Conductive dough: 1 batch per 4 people.  I prefer plain conductive dough and coloured insulating dough, since people want the pretty colours on the outside of their creations.
  • Insulating dough: 1 batch per 4 people.
  • Batteries and holders for all participants (such as one 9V battery and terminal snap per person)
  • Small motors: ideally, rated for 3V, less than 30 mA, and the lowest rpm you can find (motors that spin too fast are hard to see).  We used a 7V motor rated for 7000 rpm.  It didn’t start reliably, and when it did, it was often too fast to see, or would throw off the piece of dough stuck to the shaft.
  • Buzzers: buzzers are rated by volume and pitch.  Choose lower-pitched buzzers to prevent insanity.  We used these 400 Hz buzzers.
  • Pushbuttons and/or potentiometers, if desired
  • Extra flour (the dough gets sticky over time) (1 pile at each station)
  • Terminal lugs and crimp tool (1 tool per station)
  • Wire strippers (1 per station)
  • Decorating supplies (straws, popsicle sticks, etc.  No pipecleaners — the metal rod in the center could short out the battery)
  • Lots of LEDs: I had standard 5mm LEDs, but I love the visibility and ease of handling of the giant 10mm LEDs that UST recommends from Evil Mad Science. Different colours and sizes are nice, as are LEDs with both coloured and clear cases.
  • Safety glasses — one pair per person, especially the kind that fit over prescription glasses
  • Pencils, markers
  • Paper
  • Name tags
  • Zip lock bags
  • Bucket of soapy water, dishcloths, dishtowels (for cleanup afterwards)
  • Table cloths (and floor covering?)
  • Info to send them home with participants (i.e. where to get supplies, how to make dough)


If you’re thinking of trying this activity either at home or with a group, and you have any questions at all about choosing components, tools, etc., please don’t hesitate to let me know.  It’s quite appropriate for the electronics novice, and I’m happy to help out.

More information

Looking for more kid-friendly science and engineering projects?  Try these:

Squishy Circuits Home Page

Make Magazine


“Notes for Family Science Night” by Gas Station Without Pumps


  1. Awesome stuff Mylene. I have to try this out with my 6-year-old. I’m curious why you didn’t use resistor/5V LEDs so that you didn’t have to worry about them hooking the LEDs directly up to the battery?

    • Joss, let me guess. Did you note the part where “Any component that had been in the salt dough had its leads corroded beyond use”?
      You want super-cheap parts for this project.

      Places like Electronic Goldmine http://www.goldmine-elec.com/ have bags of 500 LEDs for $9.50 (or more assorted 250 for $10):

      “Super LED Assortment Assortment of all types, colors, sizes and shapes of prime high quality LEDS. Our largest assortment contains 250 pieces. LED colors in assortment include red, orange, yellow and green. G7436 $10.00”

      The typical price for 5v LEDs is about $25.60 for 100—over 6 times the price and you don’t get the assortment of colors and shapes.

      • That’s about the size of it. Also, I’ve got lots of LEDs on hand, so I used what we had around. We probably used 200 LEDs that evening — 20 kids multiplied by 4 colours and two sizes, plus extras for demos, etc. I let the kids take their creations home, including the LEDs, since they weren’t useable for anything else.

        Plus, I kind of like introducing kids to personal protective equipment. There’s something about needing safety gear (especially if it fits well and is not intimidating) that makes a newcomer feel like they’ve been accepted into the club. I hope that they start to think of themselves as people who do the kinds of things that require safety equipment.

        Hopefully, it sends the message (especially to young girls) that we can respond to risks by understanding them, respecting them, and mitigating them… rather than the more common extremes of either thrill-seeking or avoidance.

        If you try this, please let me know how it goes — I’m curious to know what the range of responses would be from kids of various ages/backgrounds.

  2. Thank you for posting this info. I just happen to have a group of Brownies and was searching for a way to do this both with a large number of girls AND affordably.

  3. The corroded legs could be salvaged with a few swipes with some fine sandpaper. But more importantly, I noticed my LED current drop from 20mA to 5 mA in 30 seconds because of the corrosion (only on the negative leg). This is problematic… I wonder how this might be fixed (stainless steel wire?)

    • Stainless steel probably won’t help—the chromium oxide coating on stainless steel that keeps it from rusting is not very conductive. Attaching the LEDs to stainless steel wire could be difficult. You could use alligator clips, but soldering to stainless steel would not work, as the fluxes used don’t remove the chromium oxide coating.

      Silver/silver-chloride electrodes would work, until all the sliver chloride was gone on one leg. At 20 mA on a thin wire, that wouldn’t take long, so may not buy you any time.

      Using salt as a conductor is going to cause problems with longevity no matter what you do.

    • Yes, the corroded pieces can be salvaged. If you’re working with small quantities, wiping them down with distilled water afterwards makes a big difference. I would echo the comments from GSWP below about the cost-benefit ratio of worrying about it during a single experimentation session. I haven’t monitored the current, but over the course of 60 or 90 minutes, the LEDs stay bright enough to be easily visible, which is my only requirement. A 75% reduction in current within 30s is more than I would have expected — at 5mA, I’d expect a standard 20mm LED to be barely visible, and I haven’t had that result before. Might be worth double-checking the recipe!

  4. […] that I need to do a lot of prompting. At the beginning of the year, I give a few goal-less tasks: what can you do with this conductive play-dough? What can you do with these small incandescent bulbs and AA batteries?  I give students a page […]

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