Micro - Mouse

This is a description of how I (Aaron Lager) and my partner (Micheal Witham) created our first Micro-Mouse. I'm doing this because when we made our mouse, there were not very many resources on how to make a mouse. So here goes. Feel free to email me if you don't understand anything I have presented.

First a look at our power supply Schematic
We chose Maxim because of the power savings for our battery critical application. Most people were using the good ol' stand by, 7805.
While the 7805 works great, it wastes a LOT of power. The schematic is incorrect in that it doesn't show that we were using 8NiCad cells, that's 9.6v.
In our system we were using about 300mA for the electronics, if we were to use a 7805 we would have been wasting
(9.6v - 5v) * .3A = 1.38Watts.
That's a lot of energy when running on battery power.
Our system is above 80% efficient, and we were able to debug for many more hours between recharges than our other teams were able to.

Click here for some pictures of the Square Mouse

The sensors are a two part system. There is the transmitter and the reciever.
The Transmiter:
The transmitter in its most basic form is an infrared LED (Light Emitting Diode).
We use a transistor as a switch to turn the LED on and off. The transistor is controlled by the PIC microcontroller.
The transistor is driven into saturation mode so that the maximum available current is supplied to the LEDs.
Each LED has a voltage drop of about 1.2V. I have a supply voltage of +5V. So I can string four of the LEDs
in series and still have voltage left over.
1.2V*4=4.6V drop accross one string of diodes. We use a 10 ohm resistor to limit the current through the circuit,
remember we are treating the transistor as a short since it's in saturation.
To calculate the current through a string of diodes we take the supply voltage (5V) minus the diodes
voltage drop (4.6V) minus the voltage drop of the transistor in saturation (.2V) all divided by the 10 ohm resistor.
(5V-4.6V-.2V)/10ohms=20mA
20mA through each string of diodes will light them up fairly well.

NOTE: In actual application we noticed that there was always a small current flowing through the LEDs, although not enough to light them up. A pull down resistor of about 5-10k on the base of each transistor should take care of that.

The reciever is a bit more complex, that will be next.

Aaron
aqua@ecst.csuchico.edu