L297-8

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This bipolar stepper motor driver PCB is easy to build, utilizes the STmicro L297 and L298 chips. The board is jumper selectable between full Step and half Step. It will drive bipolar stepper motors at 2A and below. Maximum voltage for the board is 45Vdc, although with motor back emf a lower power supply voltage should be utilized to give a safety margin for chip protection. An onboard adjustable resistor allows the current to be set from 50ma to 2A. The board has a 10 pin header that logic signal inputs for step, direction and motor enable, and a 2 pin screw terminal for DC power for the stepper motor being controlled by the board. Two 2 pin screw terminals provide easy connections to the motor. The onboard 5V regulator can be utilized to support external circuitry via a jumper associated with the input connector. The board can be connected to via a 10 pin IDC ribbon cable, discrete wire plugs or soldered to directly. The logic inputs are compatable with nearly all PC's and laptops, or can be controlled via a microprocessor, or simple circuitry. JP1 sets the step mode to full or half step. JP4 when in routes 5V back to the interface. Never route more than one driver's 5V back to the interface. The L298's require a heat sink as they dissipate a great deal of heat depending on motor current and power supply voltage. There are two versions of this board, the web based board for those DIY types and a commercial board I sell. This not the instructions for the boards I sell. A new DIY layout (Jan 18, 2009) with some easier to find parts and easier to etch: layout, schematic,copper parts list

Here are a couple of pictures of users builds:

Submitted by Gert Wierbos is a pdf of three of the L297-8's on one pcb. Same layout and BOM as the single board. 3axis

Feedback from one of the early users, Chris at http://timeguy.com/cradek/cnc Hi Phil,I am really happy with the boards! I didn't have any problems except with the power supply. I wanted to run at 40v which is way too much for the onboard 7805 - so I left off the regulator parts and used an external filament transformer to run regulators for the logic. At first I thought the design bordered on over-engineered because of all the filtering and schmitt triggers, but it works perfectly without any tinkering, never misses steps or gets extra steps, and so on. It just didn't have any of the problems others have when building stepper drivers. The single-sided layout is great for my PCB milling setup, since the board doesn't have to be flipped and realigned. One day I intend to make a fourth board for my rotary axis and when I do, I'll take a photo of it and put it on the site. Unfortunately I didn't photo these three and they wouldn't be very photogenic the way they're mounted in the box. Thanks for making your design freely available! Besides changing the DRC to make it work with my milling setup, I didn't make any changes and don't have any suggestions for improvement. Best regards,Chris

Upon Chris's comments I upgraded the design to eliminate the 7805 regulator limitations.

Contents

Jumpers

JP1 selects step size either full or half step. No jumper on JP1 selects half step mode. In half step the motor makes one complete revolution every 400 step pulses. Installing JP1 sets the mode to full step. In full step the motor makes one complete revolution every 200 step pulses. JP2 selects the the state for direction. There must be a jumper between the center post and one of the outside posts for direction control. Today's cnc software allows the user to configure direction travel via software, so in reality there isn't a need to change jumper setting once installed. JP4 routes 5V back through the 10 pin connector to provide 5V to an interface board if desired. Never use more than one JP4 jumper in a system because you would tie two 5V regulators together and they can fight each other and create an unstable 5V.

Current Calculations

Ohms law is R=E/I The L297 comparitor compares the voltage adjusted (via R2) to the current developed accross the sense resistor (R9 and R10). As designed 1.35V is the maximum voltage you can set via R2. For a value of .5 ohm thus the motor current then is E=I*R or Vref=I * .5. So for example a 1.2 amp motor = 1.2 *.5 for a Vref of .6. If you change the value of R9 and R10 to .75 ohm then for a .8a motor Vref = .8 * .75 = .6V.

I also sell a commercial pcb of almost the same circuit.

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More information on this drive is available in the instructions. Paul wrote me this on my commercial pcb:"I rec'd the boards today and they are NICE!!! Very good quality and looks like it will be easy to solder. I may use regular caps instead of the surface mount, though, as I forgot to order them. My conclusions? The board is fairly easy to build even with my ham fingers, and works as described. A good deal at 8 bucks, and good soldering practice for those of us who make our milled pads HUGE so we can hit them with the broad side of a barn." "I even jury rigged a 5 pin Din jack and plugged it into my Nichols horizontal mill. Was able to get 10" per minute usable feed. (I squared up the ends of some 3/4" x 4" aluminum bars for a job, .100" cut at 5" per minute, 10" rapid traverse return." "Managed to get 6" per minute rapid traverse on my Moog Hydrapoint with your board today with a 3.1 Volt 2.9 amp size 34, but had to back it off a bit on the pulse width (widen the pulse.) as I was losing a tenth or two each test cycle. Lengthened the step width 200 microseconds, stopped losing steps." "At 3.5" per minute I was able to take cuts of 5/8" wide, .300 deep in aluminum, 1/2" wide .100 deep in alloy steel. (possibly 8620, left over from a paper mill job.) This is with an Acme 3/4-5 leadscrew, and a preloaded leadnut, as I did not want to go the expense of a ballscrew just now. My timing pulleys on the axis give me a 5-1 ratio, so I am actually cooking right along at the motor shaft. Considering that I am powering everything with a 24 volt 1.2 amp wall wart, that's not too bad. I have an older Superior Electric 24 volt 6 amp linear power supply that will run all three boards well, I think, once I get everything cabineted. Or I may build something simple into the cabinet itself......I will cross that bridge when I come to it. " "Sorry if it seems I test everything to death; it's just a habit of mine acquired from years of R&D at various companies. It's all very empirical testing, anyway, I just know what I am looking for: consistency, reliability, and ease of use. Your board seems to fit the bill on all these points. I have developed several L297/298 boards over the years but they all fall down on noise issues. Your filtering schemes are just what the doctor ordered." "I have been limping along on various drivers over the years; since most of my stuff is fairly low mass iron,( for example my Hardinge lathe compound slide) it does not take much power to turn the handles. My Rockwell mill, the Nichols horizontal, the cutter grinder, all these can benefit from reliability, noise immunity, and the ability to halfstep."

The pictures are courtesy of Greg who obviously did an oustanding job constructing the pcb's.

Old Version

The information to make the original DIY toner transfer version is here: layout, schematic,copper parts list.

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