Netduino Mini based GPS puzzle box

Well, I finally completed my first Netduino Mini project - a GPS-based puzzle box for my nephew's 8th birthday. It's inspired by a couple of project I'd seen - a reverse geocache box and a steampunk compass. I'd also done a standard netduino based box similar to the reverse geocache for a friend, but I wanted to do a little better and the Mini was just perfect for it.

The plan was to take my nephew via a few locations and perhaps involve a bit more than just the GPS. In the end he had to do 6 challenges. The first 5 were to find a certain point. He had a descriptive clue and sometimes wither a distance countdown or an arrow pointing in the right direction. The final challenge was to find some magnetic ball bearings and put them on the lid, operating a reed switch and unlocking it. It all went well with only a couple of minor hitches.


Some photos










Link to full size ones.

Source code
Attached as ZIP.

The components

• A Netduino Mini - running 4.1.1 alpha 7 firmware so that I could use an SD card to store the data.
• An EM406 GPS unit (serial TTL) to track where it was
• A HM6352 compass (I2C) for orientation
• A µSD breakout board (SPI)
• A 4D systems µOLED-128-G1 1.5" display (serial TTL)
• 2 x Hitec HS-55 servos (one for the lock, one for the direction arrow)
• Cogs from a clock I picked up from a charity shop. You should have seen it. It was hideous. I've done the world a favour chopping it up.
• 3 x 9v batteries.

Things that worked well

• You may notice that I'm using two serial TTL devices (GPS and display) but the Mini has only one TTL COM port. I used both at the same baud rate and had no problems using the TX line for the display and the RX for the GPS. As far as the Netduino was concerned it was an odd hybrid device that was told to display some text and responded with incessant NMEA chatter. 4800 baud was the easiest to get them sharing. It was quick enough.

Things I'd do differently if I did it again

• Consumer 9v batteries are rubbish. They'll power the Mini but as soon as you have a couple of servos moving it all goes wrong. I was approaching a deadline so just wired 3 alkaline batteries in parallel. A better solution would be a decent LiPo battery.
• The compass didn't seem great. Continuous reading mode seemed flaky and even in query mode the reading jumped around. Having some Neodymium magnets in my pocket may not have helped!

Things I would have improved given more time

• The OLED display is a great little device. It can display images and video. It has inbuilt µSD storage that I could have used instead of a breakout. It does sound. I ran out of time to do any of this. On the negative side, readability in sunlight wasn't great - especially red text.
• Kept the servos a bit further from the compass. The magnets in the motors may not have helped with the accuracy.
• Spent more time on the wooden box. It's balsa wood stained brown and looks OK but could be better. Inside was hastily done using off-cuts and araldite.

The result
It worked really well. As his favourite thing at the moment is the film "How to train your dragon" it had a Viking theme. He pretty soon sussed out that I'd made the box and it hadn't been "left with me by some Viking who'd knocked at the door", but he played along.

The arrow went crazy at one point and pointed completely the wrong direction. Probably a bug in my code, but was conveniently blamed on crafty dragons that were trying to fool him. I wish I could use that sort of excuse at work! The second coordinate where the arrow was used it worked fine.

All up, it was weeks of effort and a far more expensive than the present it contained, but great fun to do.

Wow Fred, thats jus sooo clever and very nice thing to do for ones nephew. Haven't read all, it's huge and almost too much for me to take in. And to think you chopped it...

Very nice I like..... very clever and fun.

Wow, so cool. Best uncle ever!!!

Now I need a niece/nephew so I can build stuff like this for them.

Now I need a niece/nephew

Try on Sparkfun: for quantity there is surely a rebate and/or free shipping.

Now I need a niece/nephew so I can build stuff like this for them.

Maybe there's a reason for the effort devoted to this project..... After borrowing a nephew for this, I recently decided to just make my own. Fred v2.0 is now in devleopment with a RTM date some time in October.

My wife would kill me if she knew I was posting that here when some of our friends still don't know.

Oh congrats! Many bugfixes to do?

Fred v2.0 is now in devleopment with a RTM date some time in October.

That's a wonderful new! Will use the same MCU of Fred 1.0?
I'd expect an alpha and a beta release in the early summer.
Congrats, anyway (especially to your wife, who's making the major effort...I mean for bug fixing).
Cheers

Did you wire the 9V direct to the servos? If so, that's probably the source of your issues. Servos are 4.8V to 6V.

This is awesome! Thanks for sharing and great job.

I have a 4D systems µOLED-160-G1 too, and I have tried to use your class to use it. but seem not run, I have directly link : pin1 -> 5V pin3 -> Pins.GPIO_PIN_D0 pin5 -> Pins.GPIO_PIN_D1 pin7 -> Gnd What is wrong ?

Well done Fred. Great idea and well executed! (Project & Fred2.0) You won't have much time for hobbies over the next 16 years. Its not easy making a product that will be accepted and used by someone else - let alone a child. Shame about the 9V batteries. They are expensive and are not designed to give much current. Much better in a smoke alarm. Regards - Paul

Very nice Fred! I agree on the LiPo battery. I've been doing a lot of work and experimentation with my project. If done right, they can last pretty long and charge pretty quickly.