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First Post, Hello, Just built a my first "robot" (7029

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Jan 12, 2011
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First Post, Just built a my first "robot" &(SLA7029M)

I've just build my first microcontroller based moving-accross-a-floor object and would like to introduce myself with it. It is made out of an old CD drive case, 2x1.5A stepper motors, PIC16 stuff (MCD2 and a DemoII board ( and a driver board with 2xSLA7029M's on . It can harldly be described as a car at the moment, having only 2 6inch wheels and half a golf ball to hold the front up so far. )
This site has been one of the places I have learned a lot from over the last 6 months of fiddling with PICS, Darlingtons, H-bridges, steppers and 3phase DC motors.

I've been trying just to make my car move using Pic (16f628) to start with and LN darlington chips. I went through quite a few chips and drivers having trouble controlling the power going to it.
Looking through my many "scrapped photocopier bits" I came across this board, I think it was from an HP, it had little on it but a few connectors, an MCU, 2 large upright IC's and 1 extra large IC with a heatsink (BiPolar driver). There were some of the familiar 6 wire connectors, some big capacitors, and a groundplane. The 2 IC's were SLA7029M's and are PWM power controllers for 6wire steppers. A quick look at the datasheet and I was on its case. Things didn't seem hopeful to start, I searched on all sorts of places and there seem to be only people struggling with these chips, luckily mine was on a working board. They looked just the job, over an amp without heatsink, more probably. A look at the datasheet made it look a nightmare to start but.....

All I did was solder directly to A and B pins out of the IC's and the 2 phase-disable (tdA&tdB) pins. They went straight to into a controller (datasheet provided signal orders), then soldered 12v directly onto a big cap, and the steppers into their sockets, and bingo, off it went.! Sort of.....I had to supply the chip with a reference voltage (used a pot between 0-12v) to control the PWM level. A pain was I had to make the disable A&B inputs from the controller a very specific resistance to let the PWM work (fidling with a salvaged twin-wiper volume control. (the chip uses the disables for the PWM, when the voltage across a shunt resistor is above the "ref" mentioned that phase shuts off at khz. These do chips stay amazingly cool compared to the LN's.

So, future alterations I recon I need to look at, I intend driving the Ref pin voltage with an output from the Pic, add some proximity sensors (photocopier paper sensors), add infra-red remote support. And, a PS2 Mouse, as feedback so it knows when its stuck. Possibly a microphone too for the same purpose. If I can, I am going to make it balance too, hopefully using I2c gyro sensors, but lets see eh.!

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Hi Neal,

Welcome to EDABoard, it seems you are quite the scavenger of parts and very creative as well.

What is supplying the power to the beast?

Where did you find the stepper motors, old CDROM drives?

Good Luck with Your Project,


Many thanks,!
The PSU is just a 400Ma (2VA max) adjustable to 12v small thing. The steppers are 1.5A large-ish (2" probably) things. The CDrom casing is just to hold everything and bolt the motors and wheels to, but makes a neat package.

Everything else nearly is out of a photocopier except a few discretes and the "Pic16 Demo II" board which I got with a pic ICD (the board is 16f877 based and loads of stuff like LED's and 7SEgments and switches and easy-access MCU pin jumpers and stuff on the board. I'll make a dediacated MCU board of my own when its done. C is a language I've used for 20years so Hi_tec C was easily mastered.

A lot of stuff gets scrapped at mine printer and copier (and most things electronic) wise. I've been off work for reasons for a bit so I've been through a lot of the last few years scavanging. I'm well used to "mackeling" solutions in many areas, (smallish) electronics stuff, PC, networking, MicroSoft stuff going back to my 1st zx81.

I'll post photos when its done.!


---------- Post added at 13:22 ---------- Previous post was at 13:21 ----------

This is the motor-driver board. Apparently from an HP4500... £13 on Ebay. I wish I'd kept the wiring loom for the connectors though. I've soldered and aruldited everything on carelesly not realising I'd get it working reliably.
**broken link removed**
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