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Jøhnkes blog

Hi there.

This blog is used to document the design process involved in constructing my bachelor-project (both theory and practical stuff). I’ve now finished my bachelor-project (turned it in on the 8th of February) and have moved on to create new versions of Thing (the practical outcome of the project). I’m also in the process of rewritting/updating the bachelor-paper.

The blog includes documentation from the different Arduino/Max MSP/Processing projects that I’ve gone through (mainly my obsession with the pulse sensor). The documentation will sometimes be in the form of written-out tutorials (aimed at beginners like myself) and sometimes in the form of code examples, pictures, Fritzings (Visualized layouts of Arduino boards and connections) and other awesome documentation.

Feel free to contact me at rjoehnke@hotmail.com if you have any questions.


  • Pulse Sensor with LED connected
  • Pulse Sensor without LED connected (Fritzing, Arduino and Processing code is up – This links to the most recent one – different versions of this setup appears a couple of different places)

Final Prototype-191

Final Prototype-177


A short video showing the Poul version of Thing in action.

Thing is designed to help you calm your thoughts and help you slow down. Using infrared light, Thing can detect the pulse in your thumb and use that data to change the brightness of a red light. It’s pretty cool. The idea is quite simply to focus your attention on the pulsating light and calm your thoughts, just as one would do when meditating.

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Packaging and Printing (and more packaging)

Busy week in the lab.

Packaging Ella og Poul-225

As mentioned in the previous post Ive been trying to figure out how to make the packaging for Thing. My first attempt was making it out of wood (seen in the pictures in this post). But wood is costly and it takes time to route out the insides of the container. It also needs some form of closing mechanism. So wanting to find an alternative I decided to try out cardboard, as its inexpensive and relatively easy to work with. It also allows for printing. The downside is that its not very durable and that sucks because I’d like people to be able to easily and safely carry Thing around – to work, vacation etc. The other option is to make a box out of veneer which is inexpensive but does require some work to put together.

Nonetheless, a few days ago I started experimenting with the cardboard packaging and built my first box. I searched far and wide for a cardboard box template and found this site. I then printed out a miniature box and assembled it. The next step was to make it full size so I took some paper and started to measure Thing and draw the whole template out. See the pictures below. Oh and I also made “holders” for the box. The holders are there to keep Thing in place and also act to protect the LEDs and the phototransistor from the lid of the box.

Yesterday I went down to Art de Voss, a local art shop, and bought some paper. Then I biked on over to Godsbanen and used an hour or so to design a proposal for the packaging. I’ve been trying to rework the “Thing” logo, font type (Let me know if you have any suggestions!!) and also, as mentioned before, the names for the two versions . I was a little bit in a rush so I just decided to name them after my grandparents Poul and Ella. I think Im gonna keep it that way. The name of the version is on one end and the “production number” ie. 01, 02, 03 on the other end – I thought it be kinda cool to know what “number” Thing you have. I don’t know about that though, it needs more work. (The paper btw is 300 gsm – I think – and is 70 cm x 100 cm).

Godsbanen, besides having a wood workshop, also has a print shop, where they can print almost anything. After a long wait and a failed attempt it finally worked. I ruined my favorite paper on the first attempt so the paper color screwed up the print color a bit. Here are some pictures of the final boxes.

Friday June 28th Update:

I almost love cardboard as much as I love wood. Man it’s great to work with. To the point now I made a new box out of some stronger cardboard, the cardboard I used for the ones above is just too flimsy (realizing this having to carry it around in my bag the last few days). So stronger cardboard it is! Other than thicker cardboard I also changed the design slightly. I removed the lid and a flap from the template above, then I made a duplicate of the first one but 4mm wider and longer so it would fit as a lid. You have to check out the pictures below!

The blog

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Almost done!

Back in the lab after my trip, the last week has been spent working on finishing up the final version of Thing. Still needs some finishing touches but check out the awesome pictures below!

Final Prototype-180

A few notes on the final prototype:

– The dimensions of the final prototype is a bit smaller than the Projector version – it sits better in the hand that way

– I’ve altered the angle of the switch so it turns on/off by switching it up/down (up is on)

– Nothing is glued into place. Instead the components are held in place by small wooden spheres. I’ve done this to allow for much easier repair (with glue its almost impossible to take the components out without ruining the wood). If I have to say it myself its quite clever! The only downside is that if you apply a lot of force they slide down, but with normal use it shouldnt be a problem. And if they slide down its easy to open Thing and push them into place again. See picture below.


Now that Ive gone this far I decided I might as well try to do some packaging as well – and an instruction manuel too. Hope to get that finished within the next week so I can have a finished ‘product’. The concept video is still a work in progress – that is, I haven’t exactly started working on it yet, but I’ll get to that soon enough.

Stay safe,


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So much to tell, so little time.

It’s been far too long since the last update so here is a lengthy one!

First of all: I realize I haven’t uploaded any pictures of the handheld Thing with the a super-bright “projector” LED, so here it is!

Here’s a short video as well: Pulse Video

It’s been tested by people here in the lab, a couple of people at Godsbanen and my family. It works great :-). People tend to push down very hard on the Led and Phototransistor to begin with but with a little direction they usually get “in to the zone” after a short while. When I come home I’ll have to set up more extensive testing where I just hand them Thing, give them a very short brief and then let them figure it out. Perhaps let them inside a dark room for a few minutes and see if they can get a small meditative session going. I also need to talk to people who have experience with meditation here in Aarhus to see what they think.

Last week I finished my anthropology exam so I spent a few days in the lab working on the new version of the handheld Thing. This time the LED will be a diffused red 10 mm LED placed at the end, after the LED and phototransistor. I also decided to make a charger box (see pictures) to go along with Thing so it’s possible to charge the LiPo battery. I tested out the circuit boards and they worked fine, though it seems the strength of the LED and IR-LED aren’t as strong as the old version. But Ill experiment with that when I get home. It works and thats the most important thing! I also made a container for Thing so I can transport it around a bit easier, I also got Thing and my name engraved in it.


When I come home I’ll finish up Thing 3.0 and maybe work on a whole new mini version that I have a few ideas on – mainly trying to make it as small as possible. I also need to schedule time with the laser again as I have an idea for securing the LED and Phototransistor in place. I expect Ill have more ideas on the trip so the new version may have several new features :-)!

May 1st I set off to the Dominican Republic so the blog is going to be quite until mid June when I get back.

See you on the other side!


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Moving on and slowing down!

Last week I found out that Fritzing, the program I used in the start to visualize my circuit (so I can put it up on the blog and in the tutorial), also fabricate custom boards! This means I don’t have to solder the whole thing everytime I make a new version of Thing and I can make the boards even smaller (not that it matters that much because I can already make them small enough to fit inside the wood containers. The good thing is that its affordable too. 6 boards costs around 650 kr.- including shipping. Not bad at all. The only challenge is to get the circuit right, as my knowledge of electricity is still questionably at best.

Update: Got some help from Lasse Vestergaard to double check the circuit. I ordered 6 boards yesterday that is set for shipping on the 10th. With a little luck they’ll be in my hands on the 13th-14th. Update:

Skærmbillede 2013-04-07 kl. 20.22.54

PCB Layout in Fritzing

Also went down to Godsbanen and made another handheld box for Thing so I can put the new PCB inside once it arrives, just hope everything works once I get all the parts assembled. More on that at the end of the month. The blog will most probably be quite for the next few weeks as I have an anthropology exam due on the 22nd.

Stay safe!

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The (End)

Thing Sign-

Ok so the assembly friday wasn’t exactly smooth sailing, but, nonetheless, it has been done! The handheld Thing (really need to come up with a spiffier name for it) works flawlessly, you should see it. The original Thing is a little unstable, I’m worried theres something wrong with the Arduino Pro Mini, as I can’t seem to locate the problem anywhere else. O well, it works most of the time. I’ve written an email to Peter Friis, an engineer at CAVI who is very much down with electronics and the likes, who can hopefully help.

The plan was initially to take a break from Thing, but I really feel like going forward with it. I hope Peter can help optimize the circuit and power supply (thinking of changing the Pro Mini to a 3.2v instead of the 5v I’ve used so far, so that it can run off an 3.7v LiPo battery instead). More on that later. I’m also looking into getting the circuit printed (Fritzing, the program I use to visualize circuits, manufactures custom made boards!) Need to figure out how to set it up properly though, maybe Lasse Vestergaard (a clever fella who runs a course on the Digital Design programme) can help as he has some experience from the DUL-Radio project.

I’m also in the process of making a poster (in wood of course) for Thing, so I might be able to present it when/if that time comes. In truth this is just an excuse to try out the KERN laser cutter at Godsbanen.

Today I experimented with making a circuit in wood. Worked ok, but needs improvement. Take a look below.

Wooden Circuit-107 Wooden Circuit-113


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All’s well that ends well

Tuesday was a nightmare.

Everything seemed to go wrong in some way or another. I had a lot of problems with the handheld device. To boil it down, the lesson I learned was this: When making a pulse sensor, don’t use loctite glue. The readings were all wrong when I finally hooked everything up to the computer. Turned out the loctite had eroded the metal/shrink wrap (found this out when I, after a few hours of testing different things, decided to drill out the led and phototransistor). As though this wasn’t enough, the Arduino Pro Mini started turning off and on every other second.

It was a shitty day.

However, all’s well that ends well! Wednesday turned out much better. I got the whole thing sorted by a couple of hours of good old trial and error – testing the different components. The battery was the problem to the turning off/on problem – I even had an epiphany: maybe the walnut wood would work with the led and phototransistor placed closer together? I had thought of this earlier but for some reason never tested it out. When I did, it turned out to work! I tested out a couple of different set-ups which resulted in the led and phototransistor being placed 13mm apart instead of 19 mm – and the readings were as good if not better than before! I went straight to Godsbanen to construct a new box – I had ruined the extras I had made. While there, the walnut wood I had left fitted perfectly with a new handheld device (though a bit shorter). And as I wasn’t particularly excited about the color of the pine wood – it looked yellowish when tung oil was applied – I decided to start over with the handheld Thing. Back in the lab I drilled holes and sanded down the box and the handheld and gave them both a coat of tung oil and left them overnight.

Today, thursday, I routed out the handheld device (see picture below) and gave the box tung oil.

Started with routing the outlines of the boxes two boxes: one for the arduino and one for the battery. The two smaller ones at each end is for the toggle switch and the LED.

Began by routing the outlines of the boxes two boxes: one for the arduino and one for the battery. The two smaller boxes (can’t see them properly in this picture) at each end are for the toggle switch and the LED.

So it seems my days here in the lab are numbered. Tomorrow I count on a trouble-free assembly of both the box and the handheld. What’s left is to glue the phototransistor and led in place and test it out. I also need to drill out holes for the magnets (forgot about this until right now). After that, when (hopefully) everything works, Ill leave Thing for a bit to get back to my regular life! Scratch that, I need to make a concept video for it first.

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Handheld Thing version 1 and much more

This week, and last week, I’ve been working on a handheld version of Thing. The concept is to put all the electronics inside a rectangular box so it’s possible to walk around, projecting your pulse out into the room (see pictures).

In other news:

The pine box for Thing 2.0 is done being oiled up, so today Ill try to make time to fiddle around with putting the LED and phototransistor in it. A little worried the wood is still too dark (the end grain has turned out darker than the rest of the wood).

Handheld Thing

Handheld Thing

Getting ready to route out the insides to make room for the breadboard

Getting ready to route out the insides to make room for the breadboard

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It went wrong, again.

Assembly of Thing 2.0, 2.0, went wrong. I accidentally pressed the LED and phototransistor too far down into the box. Alas, this is not the only problem!

The main issue: is that the dark walnut wood doesn’t reflect the infrared light as well as the pine wood I used for the first version. This means that the readings aren’t precise enough. I thought I had tested this out by placing a piece of black cloth on the older version and then checking the readings (which were fine). But I guess it wasn’t quite good enough.

The solution: is to either use a lighter wood or alternatively place the Led and Phototransistor closer together, but I’m not at all sure this will fix the problem. A third solution might be to paint a white box or some other shape around the LED and phototransistor.

The next step: is to construct either the main box and the LED projector box, or just the main box, in a lighter type of wood.

Walnut almost done-92 Walnut almost done-93

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The assembly of Thing 2.0

Yo. Hello. The last few days I’ve been hard at work finishing up the new version of Thing. Today, it didn’t quite go as planned. When I tried to glue the IR-LED and phototransistor in place, the IR-LED stopped working. It got stuck pretty good in there because of the glue, so there was really no way of saving it. I think it might have been the loctite glue that did a number on the wiring. Next time Ill use the same method as the first version (hot glue). Now I’ll have to make a new wooden box, sand it, tung oil it, and pull the wiring through (took an hour last time).

On the positive side I’ve found a clever (though somewhat obvious) solution to the main box dilemma of having to put he electronics inside (My last idea was to split it in two and carve out the insides – see the last post). Instead, and this makes little sense when describing it, I’ve inserted the wires into one hole and guided them up trough the top two holes, without having to slice up and carve out the insides of the box. I then solder the LED and phototransistor onto the wires.


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Tung oil, super glue, heat gun.

The last few days I’ve been hard at work on Thing 2.0. Been down at the Godsbanen wood shop finishing up the wood and also worked a bit on the electronics. It’s coming together nicely and I’ve even made a few adjustments here and there.

To finish the wood: Ive been following instructions from this blog post. First sanding down the wood 80, 120, 220 and then wetting it, quickly drying it with a heat gun and then polishing it (removing the small spikes that come up as the wood gets wet). I use one of those kitchen pads that are dirt cheap at your local supermarket, works great. Last I coat the wood in tung oil (may be hard to get a hold of depending on where you are in the world, but its good stuff as its all natural) If you are in Aarhus, or Denmark, you can order it through these guys – it’ll set you back around 180 KR (30$)).


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