New CTEC Keycoder

I think I’m almost done with my new keycoder, it’s gone thru several iterations and I’ve ironed out most of the bugs.

I’d posted earlier this week that I’d started with a box I made out of aluminum angle, and added a bunch of momentary toggle switches, I then took the guts out of two RF remotes and wired them up inside. Sounds easy but it didn’t feel like it at the time.

The switches are mini (on)-off-(on) momentary, I really wanted to try and get sub-mini’s that just did (on)-off, but I couldn’t find any at a price I was willing to pay. I think the switches I ended up with worked out to be around a $1 each after shipping.

Space is very tight and I really didn’t want to make the box any bigger than absolutely necessary, so I ended up trimming the RF boards down and consolidating the antennas as well as removing the two batteries.

The switches center solder tabs are common and wired together

This is the spaghetti I’d created once I was “done” wiring the switches in

With being generous with the wire I’d forgotten it all had to fit in the box somehow! So I ended up shortening everything down. I also wrapped the backs of the switches and any critical parts of the boards in electrical tape.

I’d tried really hard to fit rechargeable batteries inside too, but ended up with a better solution I think. I ran a cable out and up into the battery compartment of the Futaba to share it’s battery. The cable has a Y split in it for easy removal. The RF remotes come with a 12V battery, but I’ve tested and found that they work very happily on the 10VDC coming from the Futaba. When I double checked my older remotes their batteries had dropped to 6V and were still working fine.

So, that’s my new CTEC keycoder almost done.


  • Having the antenna internally limits range so I’ll be moving it outside.
  • Total cost was roughly $94 (incl. two RF setups $60, aluminum $10, switches $24), and about 2 or 3 days of work. On the other hand the Vantec Hitchiker product is around $450 – and only works with their special Futaba 75Mhz FM 9CAP, but does have some great features that I will need a cheap micro-controller to replicate.
  • My keycoder weights in at 10oz, adding to the already heavy Futaba setup at almost 2.5lb. So I may look into making a plastic box – but the weight of the switches definitely adds up.

One last trick I learned is that you can have multiple remotes control a single RF receiver. Yep, you heard that right. I’ve been controlling multiple RF receivers with one remote for a while, but had no idea it would work the other way around – each remote doesn’t not need to have the same code even. I accidentally found this out while trying to mate the new keycoders remotes to my droid and found that my older remotes still worked.


Posted by Chris on August 6th, 2008 in Electronics | 3 Comments

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Mystery Box

Anyone want to hazard a guess what I’m trying to make here?

This photo should give it away

More photos in a few days

Posted by Chris on August 2nd, 2008 in Electronics | 5 Comments

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Charging Jack Photos

Here’s a couple of shots of my “finished” charging port and bracket and the associated wiring and electronics before I mounted it. I say “finished”, because I’m currently redesigning the circuit again to accommodate for charging two sets of batteries to work around the RoboteQ problem I experienced at WonderCon.

I ended up soldering the LED array to a small board. They were okay as standalone strings, but mounting them permanently to the bracket was easier this way. The ribbon cable on the left runs to the PICAXE board, and I braced it to make sure the wires wouldn’t pull out

Here it is installed in back of the port bracket

I added a length of acrylic to the original aluminum bracket to mount the additional electronics on it

Here’s the PICAXE board mounted. It drives the LED array

Almost done. I wired in the relay and switch that runs to the main fuse block and batteries.

The relay is hard to see, but click on the image to see the large image and the relay is on the top right of the photo

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Posted by Chris on March 9th, 2008 in Electronics | 1 Comment

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Charging Jack LEDs

I’ve been busy most evenings this month getting ready for WonderCon, but thought I’d stop and post this new addition which I’ve been working on and off for a while now.

I’ve expanded my battery charging port to include some LEDs. The flashing pattern is based on the scene in ESB where Luke and Artoo meet Yoda for the first time.

The whole thing is driven by a 18X Picaxe board with some custom code. I’d originally planned on using some simple timer IC’s, but thought this would be a good project to experiment with Picaxe.

I’ve tried to capture the LED sequence the best I could, but it’s only shown straight on for 10 seconds, and even then it’s obscured by the door some of the time.

To get to this point I had to create a new acrylic mounting plate. I still need to wire in the new charging circuit Bob helped me redesign, but this was the first step in the process.

I went through several iterations and prototypes to get it to fit and work around the Robart hinges. Hence the slots on the left hand side.

I’m hoping to fix it to the 12V charging socket and use it to mount to the metal bracket I made a few weeks ago as part of the original charging circuit.

It’s also been a steep learning curve the as I’ve not really done any major thinking about complicated electronics in a very long time.

I’ll try and post more details in a few weeks, but here’s the completed circuit after a few late nights. I may switch to a smaller Picaxe, like the 08M, as the 18X is a little bit of an overkill for this project. But the price is negotiable in the grand scheme of building a droid. I’d have to guess the whole circuit costs less $35, but in the process I had to buy a bunch of stuff to figure out how to get it to work.

Here’s a a close up of the LED matrix connected to the PICAXE board.

I also had to create a voltage regulator circuit to power everything directly from the batteries as the main power distribution board will be isolated/turned off when the batteries are charging – and the whole point is for R2 to show some bling while he’s charging right?

I ended up using a LM7805 which will step down the 12V supply to the require 5V.

When I get a chance, the plan is to eventually make the LED’s display the current battery voltage when I press a button as the Picaxe 18X has a built in voltage reader.

Posted by Chris on February 13th, 2008 in Electronics | 9 Comments

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Updated Charging Circuit

Update 4/21/08: Click here for the latest wiring schematic.

A few weeks ago, I’d posted my simple charging schematic that I’ve implemented in my Artoo. It allows me to switch between normal usage or battery charging. I’m not an electrical engineer by any stretch of the imagination, and my wiring diagram wasn’t very elegant, but the setup worked fine.

Bob Ross pointed out that I really didn’t need to isolate the ground connections in the system while charging. This would save me one relay, and power to run it. He was kind enough to redraw the simplified circuit for me, and also came up with an improved design which allows me to run my droid (low load systems) from an external 12VDC power supply while the batteries charge.

Now that I have my new 60A relays I’m hoping to wire this up over the weekend, but thought I’d share it here first.

[PDF Version]

Thanks again Bob 🙂

Posted by Chris on January 24th, 2008 in Electronics | 3 Comments

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R2 Charging Jack/Socket

I feel like I’m on the home stretch getting R2 back together. Tonight I worked on the electronics a bit more.

I plan on re-install the same three 12V 7Ah batteries. However, when the skins go on it’s going to be hard to charge them. So I’ve devised a simple circuit using some automotive relays to allow me to isolate them from the main electronics with a single switch, and charge from an external plug that will run to my Vector Charger.

I wanted to mimic something similar to how Luke charges R2 on Dagobah. The original plug used is some sort of stereo audio jack, but in real life it would almost certainly short when inserted, so I needed to find an alternative.

ESB R2 - Charging Port

After a lot of browsing various electronic and automotive stores I’ve decided to use a 12V car accessory plug and socket for bunch of reasons –

  • They can easily handle the 10-15A the batteries will pull when charging,
  • It’s hard to short the system when inserting it, even if everything is live,
  • If someone was to accidentally plug him into something unexpected – I’d rather it be a 12V device which is almost guaranteed with this type of plug. I couldn’t say the same if I’d gone with some other type of high-voltage plug,
  • Replacement parts are easy to find if I ever need to make up a new charging cable,
  • Theoretically I could plug-in and charge or run other 12V devices off of R2.

I’m going to install the charging port in the same spot as seen in ESB, and I need to make a shelf to hold everything as there’s no frame behind the hole. I cut a curved piece of aluminum that would become the shelf.

I then bent an angle in it to secure it to the new speaker bracket I made a few days ago.

Everything is held in place with just two 8-32 screws

Originally I was going to use a heavy duty DPDT toggle switch to isolate the batteries

But I had problems finding a suitable switch that would work. The one shown above was to really clunky, hard to toggle and not quite heavy duty enough to handle the potential load the drive motors would pull from the battery. So I opted to use a much smaller switch that would toggle the high load through a few standard 30/40A automotive relays. I’ll probably end up replacing these with 60A relays when I get a chance.

To mount the smaller switch I cut a small piece of acrylic and drilled a few holes that would attach it to the 12V socket plug.

I then heated it up for a few seconds to bend it into shape

I also added a status LED so that I’d know for sure when R2 is switch on

Here’s a shot of the back of the automotive relays that will do the switching. I could have probably just used one and just isolated the positive line, but I decided to play it safe and use a second to switch/isolate the ground line as well.

I’ve just bolted them below the support bracket using the same screws that holds the 12V car socket in place.

This is the setup with all the wiring in place.

When the light is green R2 is on, and the charging port is disabled/isolated from the batteries

When the light is off the charging port is live and connected to the batteries. All electronics in R2 are off and I can safely plug in the charging cable which will glow red to show it’s connected to the batteries.

At some point I may also add some red LEDs inside R2 to mimic what’s seen in the movie.

All that remains is the wiring diagram. This is the hand-draw one I worked from, but I’ll try and come back later and clean it up and verify that it matches my final configuration.

Again note – I’m not an electrical engineer so please double check everything if you’re going to try and implement what I’ve done.

Posted by Chris on December 27th, 2007 in Electronics | 2 Comments

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