[dnaman]

Roy, it looks correct to me.

What drill size did you use?

How did you make the board, toner-transfer or photo method?

[irving2008]

This is a nice and inexpensive keypad that takes custom labels.

Also available from RS.

Would be nice to have some proper labels made up, black on silver. Ideas on who/where? Anyone setup to do a small run?

[justforfun]

Thank you for the response.

I used a Laser printer and a product called Press-n-Peel, you print the layout on that material and then heat transfer to a clean PCB.

I used a #64 drill, I think that = .036" or .9144mm. I have yet to place all the parts, so it was just a guess. Once I have parts on the board I'll confirm.

Roy
Elkhart, IN USA

What drill size did you use?

How did you make the board, toner-transfer or photo method?

[justforfun]

Have not completed the overlay, but my wife does scrap booking and she has a machine called a Silhouette SD, what I plan to do is print out my layout on a color laser printer (on clear overhead film material) and then have her machine cut the items out. I plan to make a full overlay with one cut out for the LCD screen.

I'll let everyone know how it turns out.

Roy
Elkhart, IN USA

This is a nice and inexpensive keypad that takes custom labels.

Also available from RS.

[dnaman]

I used a Laser printer and a product called Press-n-Peel, you print the layout on that material and then heat transfer to a clean PCB.[/I][/I]

Toner transfer then. Nice looking board anyway. I've tried Press-n-Peel and several of its derivatives and never managed to get a good board. So I stick to the photo method now. I guess some people have it and some don't

I used a #64 drill, I think that = .036" or .9144mm. I have yet to place all the parts, so it was just a guess. Once I have parts on the board I'll confirm.

Thanks, Roy - I'd appreciate that.

[kwackers]

This is a nice and inexpensive keypad that takes custom labels.

Also available from RS.

Would be nice to have some proper labels made up, black on silver. Ideas on who/where? Anyone setup to do a small run?

That's the keyboard I use on mine - the pictures dotted around the thread (certainly in the attachment on the first post) show it.
There's a word template in there you can use to print the overlay for keypad - not black on silver though...

JustForFun:
Your PCB looks spot on. A few quick continuity and short tests would be worthwhile whilst it's empty.

Drills:
You can drill most holes with a 1mm drill - the connectors (if used) and diodes/regulator might be slightly tight but should go in.
I also use a 0.6 or 0.7mm drill for most other components, but it's nowhere near critical - just less chance they'll fall out when you flip the board to solder them...

The 82 ohm resistor is shown on the overlay - it's mentioned by value rather than by R number since you can change it to adjust the brightness of the display (less is brighter).

[justforfun]

Thanks to everyone for your input and support.

Board assembly starts tomorrow as time allows, with progress reports to follow.

Thanks again.

[irving2008]

That's the keyboard I use on mine - the pictures dotted around the thread (certainly in the attachment on the first post) show it.
There's a word template in there you can use to print the overlay for keypad - not black on silver though...

.

Not quite but very similar Steve, the one you list in the parts list, made by Multicomp, is no longer stocked by Farnell. There is an alternative , also Multicomp, now listed but its 20% more expensive than the one I suggest, made by APEM (in the UK!), which Farnell have only just (last week or so) started to stock.

[dnaman]

There are two BYV27 diodes listed in the parts list for optional areas of the PCB (Beeper and Sense/Ack). I can't scare up any of those but I do have a ton of 1N4148. Would that do?

[mp3]

The parts list says "or any switching diode" the 1N4148 fufills that requirement.

Malcolm

[dnaman]

Actually it says "Any fast switch diode".

I wouldn't know whether the 1N4148 is considered fast these days or not - which is why I asked.

Anyone?

[kwackers]

The diodes really not that critical, it just protects the transistors from back-emf.
IN4148's will probably be fine.

[dnaman]

Thanks Kwackers!

[Marty_Escarcega]

Ok, I thought I understood I could find a 24vdc power supply about 1-2amps. But a fellow somewhat savvy in cnc construction said I should have a 3.3-5 vdc power supply about 4 amps. I ordered the Chinese Stepper Driver on ebay. Should be here this week.
Specs on the stepper driver: http://www.nbglin.com/motor.htm


My steppers are Superior Slo-Syn M092 series, 3.0v 4.0amp. 300oz hold, 200 steps.

So, what do I need for a power supply?

My PC board is populated, I have my display, case, keyboard etc.

Need advice on the right power supply.

Thanks in advance.

Marty

[dnaman]

Ok, I thought I understood I could find a 24vdc power supply about 1-2amps. But a fellow somewhat savvy in cnc construction said I should have a 3.3-5 vdc power supply about 4 amps.

That's bad advice. Stick with what you thought (24V 2A).

Take a look at http://www.geckodrive.com/upload/Step_motor_basics.pdf

Read it all if you want the theory or read the section on power supplies if you just want confidence that the 24VDC number is correct.

[Marty_Escarcega]

That's bad advice. Stick with what you thought (24V 2A).

Take a look at http://www.geckodrive.com/upload/Step_motor_basics.pdf

Read it all if you want the theory or read the section on power supplies if you just want confidence that the 24VDC number is correct.

Its my understanding that the Chinese driver is not PWM. Hence the need for a power resistor?

Marty

[kwackers]

Its my understanding that the Chinese driver is not PWM. Hence the need for a power resistor?

Marty

Looking at the datasheet you linked to above it's using an L298 that's a PWM driver.

You'd be hard pushed these days to find a driver that isn't. Originally I was going to put a 298 on the pcb and drive the H bridges directly from the PIC.
I decided against it simply because it limited choice and drivers were getting cheaper and better very quickly.

[Marty_Escarcega]

Looking at the datasheet you linked to above it's using an L298 that's a PWM driver.

You'd be hard pushed these days to find a driver that isn't. Originally I was going to put a 298 on the pcb and drive the H bridges directly from the PIC.
I decided against it simply because it limited choice and drivers were getting cheaper and better very quickly.

Perhaps its that it doesn't have current limiting built into it or that the chip might have the ability, they didn't build it into this stepper driver he said it could be modified:
"I'll work on the mod and we can add it as small PCB/rework. Basically we lift pins 1 and 15
add 2 sensing resistors there, and add a dual comparator that trips at the current limit sensed as a voltage
across those resistors."

Do you see it the same way?
Thanks
Marty

[kwackers]

Perhaps its that it doesn't have current limiting built into it or that the chip might have the ability, they didn't build it into this stepper driver he said it could be modified:
"I'll work on the mod and we can add it as small PCB/rework. Basically we lift pins 1 and 15
add 2 sensing resistors there, and add a dual comparator that trips at the current limit sensed as a voltage
across those resistors."

Do you see it the same way?
Thanks
Marty

Ah right ok. It's a while since I've done any work with the 298 so I've just flipped through the datasheet to re-familiarise myself with it.
He's essentially correct - usually the 298 is paired with the 297, the 297 has comparators built in and drives the enable lines directly.

Without the comparator the issue is you either have to use a couple of high power resistors on each phase of your motor to limit the power, or reduce the driving voltage to a level that will drive the motor within the limits of both the motor and the 298.

The high power resistors are a fairly wasteful method, if you drive the motor at 2A and have a supply of 24v then 22v of that will be dropped by the resistor and the total power in each resistor will be 44W - that's a big resistor (will require heatsinking). Plus you'll need two.

On the other hand if you reduce the voltage to a level suitable for direct connection you'll be running the motor at only 2 to 4 volts (ish), you'll likely be *very* disappointed with the results...
Obviously you can go a half way house, smaller supply voltage and lower power resistor.

In my opinion, I'd look for a driver that has PWM, they're massively more efficient - since they're switching the average current drawn is a lot less than the maximum motor current and since they can run from high voltages easily then performance will be good to excellent with less danger of mis-steps whilst still maintaining a decent range of rotation speeds.

Hope this helps.

[irving2008]

I don't know how you found that board, but I'm sorry to say its a really really bad design. For a start the heatsink is much too small - probably OK for a 0.5A - 1A motor. My L298 board runs the full chopper circuitry and at 1.4A set current the heatsink (5" x 4" double finned) gets to 65degC which is close to the limits for the L298 before it goes into thermal shutdown.

This board has no sense resistors, but it is running a bipolar driver, the L298, as already mentioned so the usual Unipolar trick of a series resistor in the common coil feeds isnt really applicable, although you could put it one in series with each coil - at 1A per phase (and I'd limit to that unless you put a much larger heatsink on the L298) on a 24v supply you'd need a 21ohm resistor rated at 30W or more on each motor winding - you can't use a common one in the power supply because of the way the phases are switched - and a sodding big heatsink for the resistors to sit on. Don't expect any speed out of it tho (although for a rotary indexer thats no major issue). Also the back emf protection on this board is a couple of common bridge rectifiers, not the fast diodes you'd expect. So this board is basically good for 'fun' and education but thats about all... I hope it wasn't expensive. The reason there is no L297 is because they've got an AMTEL microcontroller on there.

Modifying this board is a complete waste of time... the sense resistors and comparators could never be got close enough to the L298 to work properly - layout on a chopper is important. You'd be quicker and easier buying a blank L297/L298 PCB from pminmo and building one from parts (and salvage the 298 from this board).