Wow – its only been a couple of days since I posted the schematic and already a question. Basically its asking what voltage regulators am I using.
My input power comes from a 7.4V pack of lipo batteries, usually about 300mAh capacity, I need 5V for my motor encoders, and 3.3V for the rest of the circuit.
The current load is fairly high, it bursts up towards 1A when the sensors are going (roughly 1/10 duty something is on). So fairly high current requirements. I also need something with a reasonable dropout , as I can run the batteries down to 6V – so a 1V dropout for the 5V line.
Putting my ‘It would be nice to get something for free’ hat on I turned to samples! I use TI for most of my sampling needs, and the REG104 series looked pretty good. Cheap linear low drop out regulators that can take some throwing around and come in fairly accessible packages.
http://focus.ti.com/docs/prod/folders/print/reg104-a.html
They don’t get too hot when running, and only require a few external parts. So meet all my requirements, so much so I always have a pile of then on standby for random project usage.
One of the biggest problems I have had when developing my micromouse robots is creating sensors which work over the range of distances required and to a reasonable resolution. I have seen a couple of mice using red lasers so thought I would have a go.
I got a pile of 20mm long, about 5mm diameter red lasers from a random seller on ebay and plugged it into a microcontroller development board with a few additions; a potentiometer to adjust intensity and a red colour sensor (TSL250R). The colour sensor is a pretty basic affair – very similar to the IR photodiodes, just sensitive to visible red light. You can get this device in 3 different sensitivities, I got all three but only tried the highest sensitivity one.
Now the main motivation to use a laser is that the beam does not expand much over distance, so instead of having some messy interplay between the cone a normal LED creates and the reflected intensity of light, there is just reflected intensity. The dot it creates does change size over distance, so its about 2mm diameter at 10mm from the lens and maybe 4mm at 100mm. But it works! I got a few volts difference on the receiver output over a 160mm range.
BUT there is a problem, not a huge one mind; Under normal circumstances when an LED sensor is looking perpendicuar at a wall the receiver is nearly always covered in the reflected light. Problem with the small focused dot is that is does not form a cone which covers the sensor. Due to the configuration shown in the photo above you can see the reflected dot on the receiver, this saturates the sensor and makes the readings nearly useless. This is overcome by mounting the receiver vertical to the laser, but a wobbly wall or ultra reflective walls could still potentially cause a lot of problems.
The other problem is the lasers’ size – they are huge and fairly heavy. I am sure there are smaller ones somewhere, I’ve just not found them anywhere. But watch this space!
Right then, a micromouse schematic. A word of warning – this schematic is for me and not for you. That means its not pretty, values are missing and circuit notes are missing.
So important parts to mention are that the Bluetooth module was from sparkfun.com and is not currently available (although there are many similar alternatives, and the schematic / pcb footprints are avaliable from opencircuits.com). The crystal value is set to some random value (around 4.2Mhz), it allows me to run at a really random clock speed (73Mhz after PLL), but gets me perfect for 921600 baud uart – which how fast I run the bluetooth module. I run both PIC’s at that speed so the intercon can be easily set up to the same speed – any arbitary setting value will work. By the way I the net I named as spi on the schematic nets are just ‘interconnects’ as they are on the retargetable pins.
Here is the pdf, you might want to use the rotate functions – or adopt a weird pose…
Public Release Jan 2011 – Micromouse Schematic
Questions in the comments area!
The mouse I have been working on up until now has been quite a complicated design as it was the technical part of my MEng Cybernetics degree. So now that’s all over its time to make things a bit simpler and aim a little lower – this is after all a hobby and I can’t devote all my time to it as I once did.
So new electronics time I think, I am going to keep the chassis and just work on my ESD and layout. I think I will keep with the two processor design as I have a couple of DSP related things I want to try with the sensors and it requires quite a lot of processor grunt to get that going. The drive electronics will stay the same, no switched mode power supplies this time, and only sensors on the front. Oh and I will keep the bluetooth – why not!
I need to design new skids as the current ones require the lower sensor pcb of the old design, so its back to Solidworks and another order to shapeways for parts. And finally – need to find some nice batteries; the ones I am using are too big and a little under capacity.
Back soon with schematic…
Not too surprising but I managed to nearly ignore my micromouse obligations for a whole year. Then again I graduated, have a job, moved house a couple of times and am only now able to say I’m settled!
So, new years resolution is to get this mouse going again, I have new designs that I have been working on and have reworked the old mouse to be less of a final year undergrad masters project and more of a weekend hobby. More to come (And a site new logo has been commissioned, watch this space).
