Here is a picture of the setup:

The main board is an Explorer 16 with a 32 bit PIC microcontroller in there. I have the prototype board connected to the expansion socket and I am then connecting this to the breadboard. On here is a 16F88 and some i2c eeprom. In the back you can see the icd2 programmer.

I have written the software for the 16F88 to act as a i2c slave, and the pic32 talks to it fine and displays the response on the LCD (although took a while to get it all working). The code to decode the quadrature signals from the motors is in there but there is a small bug in the 16F88’s code which triggers a read at the wrong time. The idea is the main microcontroller sets a pin high to make a copy of the current reading and reset the counter, this helps with working out the age of the reading. If I work out what going wrong then it should not be too long before I can plug a motor in and see how it performs…

I also have my LiPo batteries, and gears and wheels for the drive. I am waiting on a pillar drill stand then I can finish making a prototype of the gearbox, and finally see if the motors I have are up to the job!

Another year, another MINOS (UK Micromouse conference). This year I only went for the first day, the talks and testing, but was still a great experience. I got quite a few of my questions answered and am now ready to start working on my mouse proper.

The day started off well, no waiting at stations for trains and the weather was kind so I got to Egham about an hour before kick off. The first talk was on Inertial Navigation with Accelerometers from Dave Otten; is a very interesting concept as if the system works you can check to see if the wheels are slipping (something hard to detect, but can have bad consequences if it happens too often). We then had a great talk on using Machine Vision on a micromouse from Richard Nock , a bit over my head but it was early in the day and I had not looked into using sensor arrays for measuring the heights of walls.

Following was an informative talk on Pete Harrison’s mice, unfortunately as I was not around on the Sunday so did not see them run. David Hannaford gave a presentation on intelligent mice, reminds me of some lectures we have had on AI over the past 3 years at Reading.

Michael Beatus gave a presentation on his mouse to date, again not sure how well it actually did as I was not around to see it. Rob Probin then gave an excellent talk on using a camera to find the maze walls, I did something similar for a different application about a year ago and dismissed it as being too much processing for a mouse to do, but Rob seems to be making some progress, will wait an see!

Finally Tony Wilcox gave a presentation on using VHDL to build ‘circuitry’ such as quadrature decoders for mice. Interesting avenue to go down, but I think I am biting off too much with a 32 bit PIC in my design!

I also gave a small presentation on the MOD Grand Challenge, which was followed by a video from Derek Hall of his trip to India (for a micromouse competition).

Was a lot of ‘fun’, and I look forward to going to next years conference with a mouse to present! Anyhow I have already started buying new components, some Lithium Ion batteries are on their way…

First off this is all theoretical, I need some bits an pieces before I can test this outside of simulation. Hopefully in the next week or so I will order the bits I need.

The problem: Knowing where you are in relation to the walls of a micromouse maze.

The solution: Sensors.

Commonly optical sensors are used which act upon the basic premise that the diameter of a cone of light will get bigger as it travels, hence the intensity of light over a specific sensing area will vary with the distance the light has traveled. There are also other factors such as scattering and the reflectivity of the surface etc. etc. but there is a correlation, that’s the main point.

I am concerned with detecting the intensity of the light reflected, and removing any noise. My current design assumes that I have a source transmitting IR light at 10KHz and a receiver which converts received light to a current (such as a phototransistor). First I convert this current to a usable voltage, then filter it to remove the noise and then I use a peak detect and hold circuit to get the sensor reading.

You can download the current circuit diagram here: Sensor Test Board - Design 1 (Remember - untested!)

Current to Voltage

This stage is quite simple, it takes the current and produces a voltage following the rule Vout = -Iin * R. The value of the resistor should be selected based on the current expected. I chose 66K as I am considering having some digital potentiometers in there, and that’s there value. Notice that the positive terminal of the opamp is connected to Vcc, this creates a virtual ground at Vcc allowing it to go from 5V down the 0V. Because of this the voltage is now ‘upside down’ so the next bit of the circuit fixes this.

Difference Amplifier

This is a difference amplifier which takes Vcc and subtracts out voltage from it, meaning the signal goes from 0V to 5V. Although not shown here you could also add in a gain here if required. The formula is Vout = (V2 - V1) * (Rb / Ra) where Ra = R2 = R4, Rb = R3 = R5 and V1 is our voltage and V2 is shown here as Vcc.

Second Order High Pass Filter

This is a standard second order high pass filter set to 530Hz cut-off. Considering I am aiming for 10kHz modulation this is quite low, but its due to the fact that I started with 1kHz modulation. Changing the resistor values to 1K will change the cut-off to 1.6kHz which is probably a bit safer. The main noise I wanted to remove was DC and mains (50Hz), so the current values will suffice for now.

Peak Detection and Hold - With Reset

This is the one part of the circuit which is not required, but does help and remove any precise timing issues with converting the final voltage to a digital number. The two opamps create a peak detect and hold circuit. The voltage is ’stored’ in C3, the voltage here is compared with the current input on the left opamp, if it is higher the opamp acts as a voltage follower and increased the output. The opamp on the left is a buffer, I think R8 provides some current to keep C3 from discharging, its the only part of the circuit I don’t full understand yet. I added a mosfet to enable the capacitor to be discharged after the A/D has completed.

Simulation

Using LTSpice I simulated this circuit with 40uA and 50uA inputs, with a 5uA @ 50Hz ‘noise’ sign wave. Left is a small segment of the result. The dark blue signal is the output after the Difference Amplifier, the green signal is after the second order high pass filter, the red is the final output from the peak detect and hold, the light blue is the peak detectors reset signal and the pink is the 50Hz noise (scale in A and on other axis).

You can see the noise affecting the dark blue signal, and being removed at the peak of the green signal, and the result being held at this peak as required.

The complete simulation output can be found here by clicking on the following link:

Simulation Results

You can see the different current input being applied for the last two pulses.

Well, I hope this was all accurate, but if there are any issues please do email me! Hopefully I will be able to build the circuit soon and test it for real.

I have titled it ‘The Cold Expectation’

We are partially bulbless!