Step 10: The electronic circuit

VHS video - electonics parts recyclingArduino controlling a servoThe circuit for the Arduino was worked up from samples circuits from a Sparkfun kit which came with lots of easy-peasy test circuits.  

Although these covered the basics of servo control, LED brightness, signal conversion from analog inputs to digital inputs and so on, almost all of that is controlled by the code in the Arduino sketch.

The electronic circuitry for this is really absurdly simple. The inputs were simple variable resistors from old stereos, connected between earth and the 5V supply rails. The only thing that really required any electronic thinking was making sure there was sufficient current for the power LEDs. The servo circuits were really just a connection to earth, one to 5V and one to the control signal from the Arduino.

1. Using variable resistors to create variable voltages as inputs

The controls really are the simplest circuits ever. For each input needed, a variable resistor is linked between the earth and 5V, with the variable voltage output being used as the signal for an Arduino PIN. Simple!

2. Using a transistor to provide sufficient power to the lamp

The Arduino output is easy to programme, but the output rating of the Arduino Uno's digital PINs is limited to 40mA, which was not sufficient to output current or the power LEDS, which were each rated at 3W.

High power LED eyeballs being testedTransistor to power LEDsWith a supply voltage of 5V, the LED current required could be worked out using

current = power/voltage

= 3W/5V = 0.6 Amps

This meant the value of the pull down resistor that would make 0.6A of current flow from a 5V supply could be worked out using Ohm's law:

resistance = voltage/current

This worked out at = 5V/0.6A =  5/(3/5) = 5x5/3= 25/3 = 8.3 Ohms

This is obviously much higher than the 40 mA power output rating of the Arduino pins. 
Arduino LED power circuit
For this reason, instead of powering the LEDs directly from the pin (as one would in a simple "blink" circuit), the pin out put was used as a signal to a NPN transistor

Here is the detail of the rather rough circuit diagram showing the connection between the output pin (D3) to the transistor base, and the low value of the draw down resistor (10 Ohms) to allow sufficient current to flow between the 5v rails.

In theory this would give a maximum of 0.5A. This is actually running the LEDs at half power as there are two of them connected in parallel sharing the current.

The resistor used was a power resistor from a old video recorder.

3. Connecting the servos
This part of the circuit required nothing more than plugging in the servos to the earth, the 5V rail and an Arduino pin as the control signal.

<p>Great post indeed...May I ask you how much hours you spend to do it? it would be useful to compare to others..please comment ?</p>
<p>Hi. thnaks.</p><p>To be honest, I can't remember exactly. Quite a lot. </p><p>I think I made it over a few months, but doing a few hours here are there.</p>
Very nice. Thanks for sharing it!
Thanks. I've had great feedback on here. Glad you like, and feel free to reuse any ideas, etc :)
creepiest thing ever
Thanks. It does have a creepy charm. though this one may be creepier... <br>http://www.instructables.com/id/How-to-make-a-remote-control-sentient-web-puppet-b/
OMG. you've made Putin! ;D <br>great project:]]]
Thanks, and actually, you're right. It does look a tad like Putin.
ok superrrrrr
This whole project seems amazing. Except for the wooden power adapter. Thats just downright dangerous.
Thanks. It was fun. I learnt a lot! <br> <br>What is your concern about the power adapter being dangerous?
Rarely but occasionally when something is plugged in it creates a visible spark. Now its unlikely that this would ignite the wood but if it had gotten hot prior to that (say its running and there is a power surge that causes a spark) it could ignite. Basically it seems like a fire hazard to me but I could be wrong
Hi, <br> <br>your right to think about the risks when hacking kit, but I think we're safe here. <br> <br>I'm pretty relaxed that the wood won't catch fire. The plug is oak, and that wouldn't easily catch from a lit match, let alone a spark. <br> <br>The sawdust on the cable might appear more risky - sawdust can smoulder and catch if it gets a decent spark on it. However, here it is encased in latex, and is not actually exposed to the air, nor any spark diectly, so it is protected. <br> <br>Effectively, the sawdust is sealed off from the risk of any spark and latex doesn't catch fire from a spark. <br> <br>So, I think there is no more risk of this catching from a spark than the original plastic (which actually can burn but doesn't catch from a spark). <br> <br>Having said all that, you are right to check and glad you liked it. I had such a laugh making it!
congrats on the arduino challenge
hey thanks. liked your animatronic doll. the video in the park is awesome. could have a lot of fun freaking passers-by with that!
thanks :) I just recently started playing youtube videos of chucky talking through the bluetooth speaker in the doll's back pack. I need to take it out to test it on people soon :)
ha ha ha - excellent. I'm sure that it would be rather freaky to find a moving doll speaking in a psychotic voice, whilst skipping happily through the park!
Couple mistakes on your units and math.<br>It doesn't look like you're using a switching step-down converter to power your LED, so the voltage across the LED should be around 3.3v rather than 5v in your power/current calculations.<br>you state resistance = voltage/power, should be resistance = voltage/current<br>then your units are wrong in the next line. Should be 5V/0.6A not 5V/0.6V.
aha - you are indeed right about the units. It should have read A.6A - In fact I also put resistance = voltage/power, which is even worse - it should have read voltage/current - yipes!<br>Thanks for spotting this. <br><br>You are undoubtedly right about the LED. I have to say, it's 25 years since I studied electronics. I have also not accounted for the small voltage drop across an LED either. <br><br>I have to say, I generally go for as close as I can to accurate, and if it works, just get happy like a dog with a bone. Not very scientific I concede :)<br><br>Anyway, thanks again for this. I have amended the unit typo accordingly
I just looked at it a little more carefully.. Your current is actually going to be (5v-vdrop)/r. Vdrop for white LED's is at least 3v generally, plus there will be some drop across the transistor, so you're really looking at more like 150-200mA total, or 75-100mA each.<br>Also, specifically when dealing with LED's (especially power,) you should run each of them with a series resistor, rather than one for the pair. Running well below their rated current it doesn't matter so much, but if you wanted to push these, you'd be best off using a power transistor or FET with the emitter/source tied to ground, then two resistors (about 2 ohms each) to the collector/drain, then connect one LED cathode to each resistor and the anodes to +5v. The LED's would need sizeable heatsinks, and you'd need to use 2+ watt resistors in this configuration though.
You can make a head using this instructable: http://www.instructables.com/id/Making-a-cardboard-head-with-a-secret-hiding-spot/ <br> <br>It seems to be perfect for this...
Wow - that is an awesome job they have done on the cardboard. Really impressive.<br><br>I toyed with doing thinner layers, but didn't have the laser cutting kit, so it would have had to have been by hand. I also like the carving process so I deliberately only used the layer sample as a general aide/guide, not a definitive copy. I like the idea that in theory I could make anothercopy from the original templates, but it would be subtly different, because it is then hand finished. <br><br>I'm off now to patch them for that. It's really great. It deserves credit<br>Thanks for sending the link
Yup. We all dont have access to a laser cutter. And most of the awesomest instructables coming out require that...
what brand of roll on did you use? im planning on replicating your eye mechanism and your mechanical control idea is really brilliant all the other techniques i have seen use some sort of gimbal this is exactly what i am looking for thanks so much and do you have any better images of the attachment points for the servos between the control rods and the brake wire?
Hi.<br><br>glad it was helpful. I struggled with this in a few prototypes, so if you don't have too, then that's a bonus.<br><br>The make of deodorant probably doesn't matter too much. i suspect they are all made by one big factory with different labels. I tried several (just because I had a few I had collected over time) and they all worked the same. I suspect, just cheapest supermarket own brand is fine. Just use two of the same make, so they match.<br><br>Photos are here: <br>http://www.flickr.com/photos/rosemarybeetle/sets/72157627007433214/<br><br>some are already in Step 8 of this instructable but there are a few extra ones. For the wire and servo, think of an old steam train wheel with the drive rod, but in reverse - It needs to transfer the rotary action to up/down:<br><br>http://www.flickr.com/photos/rosemarybeetle/6133065281/in/set-72157627007433214<br><br>Hope it all goes well
i would have used a skull and red leds that would be epic
Or make something like Crypt Keeper from Tales From The Crypt - http://www.youtube.com/watch?v=m-e8ATuFpIc<br><br>The eyes would go well in something like this http://www.youtube.com/watch?NR=1&amp;feature=endscreen&amp;v=Q0lecWPcMU4
That coud work. I have to say, that I quite liked making it look like a (fairly) normal head though. It's more unsettling :)
More accurately a wooden head with animatronic eyes... yes? When I saw he title, I had so hoped the head/face would move, especially when I saw the slices.<br><br>Maybe next time.
Hi. <br>I guess that's a fair point! Sorry to dissapoint. This was a first attempt, so I deliberately tried not to push it to far. <br><br>Since completing this one, I have had been pondering mouth controls - some sort of sound to motion controls which move the lips etc based on sound. I've done it with Flash before, but not physically.<br>. For outputs, it would need the basic mouth shapes to be worked out and then made possible with controls, and for the inputs, I was wondering if it could be driven by the audio out from any iPod/mp3 player, etc. It would be funny to have a head that detected the voice part of a song, and &quot;sang along&quot;. It would, of course need to do so in a slightly bizarre and unsettling way :)<br><br>I need to lie down and rest before I start that one though!<br><br>
You would probably get some great ideas from this video which has prostatic singing heads. Not my <a href="http://steampunkwayoflife.blogspot.com.au/2012/02/beautiful-prosthetic-singing-heads.html" rel="nofollow">creation</a> but I wish it was!
That is awesome. Thanks, The heads don't actually move - it is projected video, but it looks amazing. I have done this with multiple over lapping unsynced super 8 projector loops (yes film, I am that ancient!), and it is really surprising how effective it is.<br><br>A shot of how that was set up showing retro-tech (even in the 1990s, this was way old kit!!)<br>
Now my bubble is burst! I should have noticed that! The best one I have seen is a face projected onto a tree at night and only the eyes were moving!
They are still amazing though. It took me several views to work it out, and I bet they scared the proverbial out of anyone who turned up!
The link would be useful - here it is<br>http://www.flickr.com/photos/rosemarybeetle/3293092574/
That's quite a gallery you've got there. You got me at fries and strawberries. You've nailed Punch! Love giant bird and the gargoyle chair is awesome! Did you make all of these? Was that a picture of you in the seventies with long hair?
Hi. thanks. I'm flattered.<br><br>Yes I did. The chips tasted even better than they look - yum<br><br>and, yes - that is me with long hair sticking out of half a very large bird. It was the nineties though, not seventies<br><br>
Great build! I've emailed my partner about this, hopefully she'll let me create one for us!
Thanks - the links you sent below were great too. The steampunk blog was amazing
now place it in a corn field with radio control and freak people out =D<br>it's an alien invasion.<br>nice build!
Ha! Yes radio control is a great idea. I had alo an idea to have a remote control text- to-speech mouth operation. Ths was actually just too much to complete, but the idea was that you could type sentences and send to the head which would speak them. That would be freaky
since it is a (freaky) reading lamp, you could have it read your book. for people with a loss of vision, (with a usb stick and a laptop or other thingies)<br><br>personally, I have one eye which is almost blind and the other compensates it by being close to perfect. If I would only be able to see with my bad eye, I could still defy a talking head with glowing eyes (and a talking mouth), which is always fun to watch, so I would buy it ;-)
Yes, text to speech of a USB would be amusing. It would need an unnecessarily dark vocal tone. Something like batman in Batman Begins!
Putin is very similar. :-)))<br>http://en.wikipedia.org/wiki/Vladimir_Putin
Blindly. You're not wrong there! That's uncanny. Image me laugh!<br>Thanks
@Rosemarybeetle; Tweeted! Love the timelapse effect in the video. Cheers : ) Site
Thanks.<br> I'm glad you like the vid. I thought it was the fastest to give an idea of the entire process (even though I does miss out a few bits!)<br><br>Tweeting very much appreciated. Thanks you
I really like this. Weird, wonderful, and a great detailed blog of the build. Enjoy ! I will have to have a go at a weird head!

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Bio: I like making all sorts of stuff, out of found materials: furniture, wild food, whatever! I've learnt loads from generous people out there, so ... More »
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