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GPS puzzle-box project


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#1 Fred

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Posted 09 December 2010 - 03:59 PM

I'm just about to start a project and thought it was interesting enough to share and to get some comments and advice. A colleague is planning to propose to his girfriend and he wanted to do it in an original way. But you probably want to know where the Netduino comes in...

The plan is for a small box that's locked. It will only open in a specific location (GPS obviously) and can give some hints (probably a 2-line LCD display) on getting there. Once she's there the box will open and there will be the ring - and her other half. The inspiration from this was a guy who did something similar as a wedding present. Can't find the link right now. [Edit: Here it is.]

A nice neat little box would be ideal, so the Netduino Mini fits the bill. I'm UK based so I'm thinking about something like this GS module from SKPang. Hoping to keep things simple so a serial enabled LCD like this.

So, if anyone has got any useful tips please jump in. Off the top of my head:
  • What GPS / LCD unit is likely to work best
  • Whether I'll have any issues trying to use 2 serial devices on the Netduino


#2 JonnyBoats

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Posted 09 December 2010 - 06:01 PM

From a hardware hacking standpoint a GPS module like you referenced is cool, but from a cost point of view it may be cheaper to use an off the shelf consumer GPS either hand held or designed for a car. Here in the states one can buy a TomTom or Garmin really cheap these days. An added bonus with a off the shelf GPS is that it has a display built in.Further you could have the NetDuino load the coordinates of the waypoint to the GPS (or just do it on the GPS itself) and the display on the GPS would show the distance and direction to the waypoint. This way you may be able to get away without a separate LCD display wired to the Netduino. All you really have to do is have the Netduino check the information coming from the GPS and unlock (solenoid ?) when it "arrives" at the appointed spot.

#3 Chris Walker

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Posted 09 December 2010 - 06:03 PM

Hi Fred, The Netduino Mini has two serial ports, but one of them is RS232-level. Also, you generally use one for programming--so if you do use a Mini you'll want to prototype this on the Netduino and then move it over to the Netduino Mini "when you're done". Since you won't be able to debug _and_ use both serial ports at the same time. Chris

#4 Fred

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Posted 09 December 2010 - 06:27 PM

Jonny - Not sure a consumer GPS is the way to go, as how it looks is pretty important. I did consider doing all the work (UI, GPS) on a smartphone and opening the box via Bluetooth, but that just wouldn't be right somehow. I do have an old TomTom bluetooth GPS unit though. It might be worth taking that apart for a look. Chris - good tip about prototyping on a standard Netduino. Would it work simply dividing down the voltage from the RS232-level port with a couple of resistors if it's being used for output only?

#5 Chris Walker

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Posted 09 December 2010 - 06:54 PM

Jonny - Not sure a consumer GPS is the way to go, as how it looks is pretty important. I did consider doing all the work (UI, GPS) on a smartphone and opening the box via Bluetooth, but that just wouldn't be right somehow. I do have an old TomTom bluetooth GPS unit though. It might be worth taking that apart for a look.

Chris - good tip about prototyping on a standard Netduino. Would it work simply dividing down the voltage from the RS232-level port with a couple of resistors if it's being used for output only?


Fred,

If you're just using the RS232 for output, you should be able to convert the voltage "signal". Also, you may consider using an LCD which uses SPI...

Please note that RS232 is -12V to 12V, not 0 to 12V.

Chris

#6 Fred

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Posted 16 December 2010 - 11:15 AM

Definitely a good idea to prototype on the standard Netduino, especially as I'd planned to use TTL serial for debugging the Mini and that's what the devices I've got want to use too. I got the Sparkfun SerLCD working and I'm also receiving data from the GPS module. Then I had a sneaky idea... I only need to transmit data to the LCD and receive data from the GPS. I should be able to get these both working at the same baud rate, so why not share the single TTL serial port on the Mini for both? From the Mini's point of view it's a strange mutant device that likes to receive "Hello World" and replies randomly with NMEA strings. I'll let you know whether it works.




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