Older blog entries for earlwb (starting at number 4)

Atmel Atmega8 and Atmega128 MLF package MCU's from digikey or Pioneer are finally available in some small quantities. A Atmega8 MLF chip is about 5mm square, really small. I ordered some, I hope to shrink my nano-sumo robot PCB's down to one PCB with the MCU, dual hbridge motor controllers, and really hopefully maybe even the 1.2v to 5v DC-DC converter all onto one under 1 inch PCB. Currently, my nano-sumo PCB has a MCU board, two motor controller boards, and a DC-DC converter board. I actually use a LM2621 DC-DC converter that puts out about 1 amp max, so I use it to drive all the electronics including the two tiny motors as well. Then I can use one nicad or nmh battery cell just like the little Microsizer RC cars.

Bad luck building up my Can Can DPRG contest robot. One of the ESC's appears to program but not drive the motors. One ESC works and one doesn't. So I have to send it off to get fixed and wait forever for them to send it back. I hate it when that happens. New right out of the box. I guess I should just stick to building my own motor controllers, at least I can fix them myself.

Last week I was successful at building a second Gyro/Accelerometer combo board. And it works as well. It was a little scary at first, as I accidentally caused a short on the gyro chip and had to remove the chip, clean up the chip and the PCB and resolder it back down. In this case I used a ADXRS300 chip with 300 gegress per second performance versus the earlier PCB using a 150 degree per second chip. Those hot air SMD rework stations are worth their weight in gold.

It was a busy week, I got most of my new balancing robot built up. I made up a PCB co-processor board using a Atmel ATiny26 MCU to use with the gyro combo board, and I also got the Atmel ATMega128 MCP main PCB built up and tested as well. Now comes the fun part, wiring in all the stuff and getting it all programmed. I am using two of the new Hbridge motor controllers from NewMicros and I'll be running the motors using 16 NMH AA cells for about 19.2v. The plan is to have the ATiny26 read the Gyro and accelerometer chips and keep the robot in balance. The Atiny26 will also monitor the serial port for commands from the main MCU. The main MCU will tell it to go forward, reverse, slow, faster or turn left or right as needed. I've mounted a couple of encoder discs to the wheels with encoders so I can get distance traveled information or RPM indications as well. Lots of little things to do now.

Sorry I was so excited that I forgot to mention that this is the new Analog Devices ADXR150 Gyroscope IC and ADXL202 Accelerometer IC.

It's alive, It's Alive!!

I was successful at mounting my Gyro chip on a PCB. Plus the circuit works too. Really, really neat. I had a PCB layout done for me by ExpressPCB.Com, I then applied some flux onto the PCB and carefully placed the chip. Then I used a hot air rework station to carefully heat up the stuff and solder it down. Of course you have to carefully hold the chip in place to prevent it moving as the hot air flows under and around it. It took about three seconds to heat it up real nice. You could tell as the solder started flowing as the chip would drop down ever so slightly.

I am planning a project submission for the DPRG website detailing my PCB layout for a combo low cost Gyro/Accelerometer system on one PCB.

Of course low cost is relative. Right now the Gyro chip costs $39.90 in single units, and the Accelerometer costs about $29.90 in single units as well. So we have about $20.00 for the PCB (piggy back with other layouts), $70.00 for the two chips, plus maybe about $10.00 for other assorted parts like capcitors, inductor, regulators, connectors, etc. So it looks to be about $90.00 or so, to build one up. But then a while back another company wanted something like $4500 for a gyro chip setup. So in that case it is low cost.

But it is really cool, works nice, the gyro is real fast and very sensitive to small tilt changes. The Accelermeter allows you to compensate for the creeping gyro errors that occur in things like a two wheeled balancing robot.

I love it when things actually work. It is so hard to debug and fix things in the unknown never been there before area.

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