IC Pitch conversion?

Hi, Clifter. Your Allegro 3967 is a 24-pin SOIC (Small Outline IC) with 50 mil spacing. I'll bet you wanted something in a standard DIP package with 100 mil spacing, right?

Welcome to the world of SMT prototyping.

The good news is there is an easy-to-use "store-bought" solution. The bad news is it will set you back a few bucks. Thaake a look on page

342 of the current Digi-Key catalog, and find the 24-pin Aries Surface Mount SOIC-to-DIP adapter, Aries P/N 24-350000-10, Digi-Key P/N A322-ND, for $4.71 USD ea.

All you have to do is solder the SOIC on the board in the middle, and you can just plug it in to your 0.1" spacing protoboard just like a standard 24 pin DIP.

For the 3967, start out with the manufacturer's data sheet and app notes on this page:

This is a significant IC indeed, but provides a good solution if you need to microstep at 1/4 or 1/8 steps. If you only need to do full or half-stepping, it's a little much.

There are all kinds of PIC support groups online which can help you get started.

Good luck Chris

Hi Chris Thanks for the info! Just what I needed. I picked the 3967 just because it was the only chip after the 5408 that is well documented on the net for driving steppers. Can you name any simpler drivers that would work? Which group should I check out? Thanks, Clifter

Hi, Clifter. There are traditionally three parts to making a stepper motor go:

1) The indexer, which typically provides either CW/CCW pulses or a Step pulse and a direction signal (step and direction are inputs to your IC). I guess you were planning on getting those from your PIC. 2) The translator, which does the logic conversion of the incremental pulses into the information of which phases of the stepper motor are on (and if you're microstepping, the duty cycle). 3) The driver, which converts the translator output into high current (and sometimes higher voltage) pulses which actually drive the motor.

Your Allegro IC does 2) and 3). If you're only interested in basic movement of a stepper motor, you can get away with a much simpler setup. Actually, if you've got unipolar drive (one end of each of the four coils connected to Vcc, and switching the other side to GND), and you're only interested in full stepping, you can do 2) and 3) with a couple of CMOS ICs and four power darlington transistors -- really simple. If you want even simpler, and you've got 4 pins available on your PIC instead of 2, you can just look up which phases are on for the next step, use your PIC for 1) and 2), and just turn on the four NPN Darlington transistors with the PIC outputs, which will act as 3), the stepper driver. You'd also need a few resistors, but that's by far the simplest way.

OK. If you want to know, you've got to pony up some information -- there are just too many options. Answer these questions, and you can get a good answer:

• Coil voltage

• Coil current

• Unipolar or bipolar drive?

• Full step, half step, or microstepping? (Your IC is overkill unless you need 1/4 step or 1/8 step microstepping)

• Would you like to just run it directly from your PIC (i.e. full or half-stepping?)

Feel free to post again if you'd like more information. By the way, if you'd like a little background on stepper motors, you could do a lot worse than glance at Jones on Stepping Motors, the classic web stepping motor resource:

Good luck Chris

Wow, what an incredibly thorough response.

I was planning on using the PIC for 1) The indexer. Given that the Allegro 3967 is only $4, ready to go, I do not mind having an over-engineered solution to 2) and 3), ie running the stepper motor, especially since I am a total breadboard/IC newbie, don't know what darlington drivers are. But maybe hooking up the 3967 is trickier than the darlington? Also, 3967 is presumably an advanced mitigator of that infinite voltage effect.

Motor: Japan Servo KP4M4-029 Unipolar 1.8 degree 12VDC Stepper Motor. Current: unknown, until I test the motor Application: (Gear-reduced?) Rotary actuator to open and close a vent: Run clockwise a few revolutions (more or less depending on other inputs to the PIC), hold for a few seconds, then counterclockwise as many revolutions to close the vent (or until a limit switch is hit) I think I only need fullstepping. I will look at the Jones on Stepping Motors. Thanks so much!..! Clifter

Hi, Clifter. Glad to be able to help.

If you've got a 6-lead or 8-lead stepper motor, and you're not interested in blazingly fast rotational speed, you can use unipolar drive (Vcc = 12V), and do this (view in fixed font or M$ Notepad):

| VCC VCC | + + | | | | .-----------------------------------------------. | | ___ | ___ ___ | ___ | | | .-UUU-o-UUU-. Stepper .-UUU-o-UUU-. | | | |Ph A Ph B| Motor |Ph C Ph D| | | | | | | | | | | | | | | | | '-----------------------------------------------' | | | | | | | | Q1-Q4 | | | |/ |/ TIP101 |/ |/ | .-|Q1 .-|Q2 .-|Q3 .-|Q4 | | |> | |> | |> | |>

| | | | | | | | | | .-. === .-. === .-. === .-. === | | | GND | | GND | | GND | | GND | | |1.5K | |1.5K | |1.5K | |1.5K | '-' '-' '-' '-' | | | | | | Ao----' | | | | Bo----------------' | | | Co----------------------------------' | | Do----------------------------------------------' | (created by AACircuit v1.28.5 beta 02/06/05

Connect A, B, C, and D to four PIC output pins, get 4 ea. $0.01 1.5K resistors and 4 ea. $0.75 TIP101 transistors from Mouser, and you're good to go. Your whole driver will cost less than the SOIC-to-DIP socket I mentioned earlier, and everything will fit on your 0.1" protoboard.

Can't beat this for simplicity and ease of use here, eh?

Look at this simple circuit, read Jones on Steppers for some of the technical stuff, and feel free to post again if there are any problems. If you can use unipolar drive, and your stepper coils need less than an amp or so each, you're done here.

Git 'R Done Chris