MouseAir Version 2 PCB Submitted

I’ve now converted from hand wiring to doing Printed Circuit Boards for building projects.  The prices for small (5cm x 5cm) 2 layer boards has fallen so far (around $20US – includes shipping – for 10 boards) that it just isn’t worth it hand wiring a prototype board.  I’ve been doing the hand wiring of protoboards for many years and the technology, cost and delivery times for small PC Boards has changed to the point where I needed to move ahead with the times.  Note the cool use of the MouseAir logo.

What is this Board?

This MouseAirV2 Connections PCB is primarily a connecting board between the Raspberry Pi and all the various motors and servos of MouseAir Version 2.  The top connector (JP1) goes to the Raspberry Pi B (I am putting in mounting pins for the B+ but you will have to either have a special GPIO cable on the B+ or clip off two pins on the B+ to allow the older style of cable).  JP10 and JP11 allow more connections to the GPIO Raspberry Pi connector for user customization.

MouseAir Servo Motors

Along the left side are four Servo connectors.  Two for the Pi Camera tilt/pan, one for the mouse ramp loading mechanism and one to push the mouse between the motors for firing.

These are connected to GPIO pins in the Raspberry Pi for software PWM using the RPi.GPIO library.  Because the Raspberry Pi uses a preemptive operating system (Linux), software generated PWM is a little dicey.  I use software PWM for the one servo motor (Kitty Litter Cap Shutter(tm)) on Project Curacao, and it works fine, but I do have an analog feedback device to see where the servo ends up and then I adjust it for error.  I believe that I can position the servo motors on MouseAir by using the software PWM without feedback based on my experience with Project Curacao.   None of these motors needs to be positioned particularly accurately in a short time.  Experience will prove whether this is correct.  I have added an additional I2C port (JP7) in case I am wrong (to stick on a Servomotor I2C controller).

Power for the PC Board

There is one SMD part on this board.  It’s the mini USB connector on the right of the board.  I’ve purchased some solder paste and application tools.  I’m looking forward to putting this connector on the board.  Maybe.  The board, motors and servos all use the on board 5V from the USB port.  I got away with using the main 5V supply on the Raspberry Pi for the Servo on Project Curacao, but I won’t be able to do that with two motors and 4 servos on MouseAir.

What Else?

There is a connector for the Ultrasonic sensor (to detect the cat) – with a voltage divider to talk back to the Pi, the relay (there are a number of ways to do this, but these relays were cheap)  to apply power to the motors with diode protect for the inductive kickback and the screw terminals for the motors.

How Was This Built?

I built this board using the free version of Eagle.  I tried a number of other software packages, but finally I took the dive and used Eagle.  It has a learning curve, but it is worth it.  It has a large set of device package libraries available from a number of different vendors.  For this first board, I used a Prototype PC Board manufacturer called tinysine and it should arrive next week (using $4 Hong Kong Post).  Total cost?  $17.50.  Even with the learning curve on the Eagle software, it was worth it.   This first board took me about 8 hours to do (I had to learn all the software, find the library, design the schematic, etc., etc.) but the next board (for WeatherArduino, my next project – more on that next week) only took 3 hours from start to shipping the Gerber files (this second time, I sent it to dfrobot.com and paid for DHL ($12) for a total of $24.50.  I should have that board in a few days.  I’ll report the statistics and the quality of the boards in an additional posting when the boards are here and wired up.

What’s Next for MouseAir V2?

I’ll do some small modifications on the 3D printed box for MouseAir V2 and then install the PCB and start the final debug – not just electrical debug, but the mechanical debug.

The entire loading and firing system has not been integrated yet.  The system is bound to need some tweaking.  Again, I am going with the less furry mice to keep things simple.