In this series’ third post I describe the electronics involved in the Frustromantic Box.
The electronics involved in the Frustromantic Box are pretty straightforward. I hooked everything up on a SparkFun Protoshield based on the instructions here, which I think are slightly out of date now. I think the attached block diagram explains everything pretty clearly, but here’s a bit more detail: apart from the Arduino’s I/O pins, the connections form two power planes and a ground plane. The 6V output of the Polulu switch runs the Arduino (which I guess regulates it to 5V), the servos and the illuminated switch. The 5V output of the Arduino powers the LCD display, the GPS module and the IR receiver.
The block diagram doesn’t show the power supply. I used 4xAA’s, which hook up to the GND and VIN pins on the Polulu switch.
I had a real problem processing the output of the PNA4612 module when the batteries are even slightly discharged. This might be something I could correct in software, but if I were doing it again, I’d probably just run a barrel jack through the side of the box, similar to what Mikal did on the original puzzle box.
By the time I got the electronics finished up, I was running out of time before Christmas. Rather than solder everything to the prototype board, I just left it on the solderless breadboard and epoxied the $*#% out of it.
Continue to Part 4: Software
I was trying to hook up the LCD based on your diagram here and ran into a couple of problems:
The backlight on the LCD usually runs at 4.2V. You need to add a 5.7 ohm resistor between the 5v and the backlight power (BL+ in your diagram) or the backlight LEDs will burn out quickly.
Also, on the LCD you need a 10k-20k potentiometer going from Vo to 5v to set the contrast. See http://arduino.cc/en/Tutorial/LiquidCrystal Without it I the contrast was all the way up and I can’t see any of the letters. I suppose you could fix the contrast with a 15k resistor.
Whoops, you’re absolutely right. I’ll update the diagram.
hello
i would also like to build a reverse geocache box but i am still with a few problems or well ..
isnt the gps module verry exposed? why dont you try putting a tiny square of plexi on it? i guess that will not block the signal that mutch
isnt your arduino unstable?
as since the arduino gets less than 7v it will be unstable and the 5v rail will be less than 5 v
(according to arduino.cc )
thank you diamantmatch
Hi!
Yes, the GPS module is pretty exposed… I think it would probably work OK even if it were inside the box, but I haven’t tested that.
And yes, the power is definitely a problem. If I did it again I would definitely upgrade to the Polulu PushButton Power Switch SV instead of the LV, and then power it from a 9V battery.
I had similar problems with the power especially while driving the servo. I ended up using the polulu SV and used 5 tagged lithium AA cells to provide sufficient power.
I used a serial LCD because I had one spare but ran into problems with interrupts while using software serial and software servo. I would get some servo twitch while writing to the LCD.
I used one servo (centre neutral) to open two separate lids over three gps locations. (the First and last)
For a backdoor key I used external power along with a two way voltage divider read by an analogue pin to provide unlock or full reset options.
Cool! Any pics to share?