Copying Simple Circuit to Drive Step Motor

[the0wn4g3]

Hi,
I need help copying a simple circuit to drive a bipolar step motor in 1 direction. I have the 16HY0405-08 motor (specs here: http://www.dalpac.de/16hy.htm) being driven by this circuit: http://i4.photobucket.com/albums/y11...ircuitcopy.jpg
I'd like to just copy this circuit because I know it works perfectly for my application. I have all the parts, but after prototyping the circuit on a breadboard to the best of my ability, the motor doesn't function at all. I have limited prototyping knowledge, so I must have messed up the circuit some way.
Is there a simpler circuit that would achieve the same result? (about 5 RPM in one direction)
Or is there any way I could post pictures of the breadboard and let someone find my mistakes?

Thanks

[irving2008]

Can you post the schematic and the parts you have used (or a link to them).

What test equipment do you have (e.g. multimeter, LED probe, etc.)

What is your level of electronics expertise?

[the0wn4g3]

Ha! I guess that information would help a little, wouldn't it?

Here's a picture of the circuit I'm trying to copy:http://i4.photobucket.com/albums/y11...ircuitcopy.jpg
Here's a schematic I made (I'm 95% sure everything's right):http://i4.photobucket.com/albums/y11...e/unnamed2.jpg

I have a multimeter only. I have a very basic understanding of electronics, but I can learn pretty quick. I'd never heard of Eagle layout, but I managed to stumble through the schematic maker, so yea
I have everything in the circuit already. I can write up a partslist later today.

Thanks.

[irving2008]

What is the 'driver' chip. I'm guessing the 8-pin chip is a 555 timer. What is the supply voltage on the 2-way connector, I assume the +ve is to the right (black/white wire).

I can see at least 3, possibly 4 issues... but I'll wait til I have all the info first...

Do you have a photo of the rear of the board? Is that a working board?

[irving2008]

OK I worked out what you intended.... your schematic is a bit garbled... I will post a clean one soon when I have got out of my next meeting...

[the0wn4g3]

Awesome. Yes, the board I'm copying is working fine. The driver is a MC3479P (datasheet: http://www.datasheetcatalog.org/data...ola/MC3479.pdf) Yep, the 8-pin is a simple 555 timer. +ve is to the right. I believe in input voltage is 7.5V, but I could be wrong. I can check when I get out of class. Here's a photo of the back: http://i4.photobucket.com/albums/y11...e/DSC02752.jpg

Haha, sorry for the garbled schematic. I've never made one, so I'll take garbled for a first try

Thanks SO much.

[irving2008]

going to be tomorrow now.... watch this space....

[irving2008]

I have to say that I can't see how that original circuit would ever work. Are you sure thats a 555 timer? because the way its wired up it has no power to pin 8 and the reset is permanently held low.... and there arent enough parts to make it run as an astable pulse generator which is what I assume is intended!

Anyway, I have sketched a circuit that will do what you intended.... which is to drive the motor continuously in one direction...

I'll add some thoughts on values later...

[the0wn4g3]

Wow man, you are awesome! I can actually follow that schematic much easier. Should be a ton easier to prototype.
The original circuit definitely works. It comes on a piece of marine aquarium equipment called a kalkwasser stirrer, from a very reputable company. It constantly stirs a powder called kalkwasser, to keep it from hardening, which maintains calcium and alkalinity levels in a reef aquarium. As you can see on the site, it's like $700. No way I'm paying that, so I've been researching step motors to build mine own!
I don't know all the inner-workings of the circuit, but you're right about pin 8 not being connected to any power. I never even noticed that before. Now where the big hurdle for me is figuring out values. Obviously if I can find the exact step motor I can copy this circuit exactly. Odds are though, that won't happen. Are there big circuitry difference in say a 7.5V .4A motor and a 12V .42A motor?

Thanks again! You rock! It much easier learning things from people on forums than it is reading on websites.

[irving2008]

Looking at the original circuit, it has a large diode across the supply rail. What is the part # of that diode (the big black one). Are you sure its a DC supply and not an AC one?

What are the values of the resistor and capacitor above the 555?

I still can't see how that's supposed to work - I am convinced this isn't a 555, as pin 8 (Vdd) is not connected and pin 1 on a 555 is 0v yet here it is connected to the + rail.

Moving on to other things for a moment... for the circuit I show, to achieve 5rpm on a 1.8deg stepper motor you need a pulse rate of 5 x 200 steps/min = 16.7 pulses/sec. The appropriate values are R1 = 10k, R5 = 8.2k and C2 = 3.3uF. For more info on using a 555 timer look here.

The resistor R3 drops the supply voltage to enable the 6v zener diode to regulate the supply to the 555 and keep the speed reasonably constant. The 555 draws about 6mA and the zener needs a small bias current so assume 10mA in total. The resistor R3's value depends on the supply volts. Assuming 12v then a value of (12 - 6)/.01 = 600ohm (use 560ohm) will do. The wattage dissipated in the resistor will be 6 * .01W so a standard 1/8 or 1/4W resistor will do.

The only other part is R2 which sets the output current in the motor coils. The motor is a 0.4A motor with a 30ohm coil (i.e. nominally 12v) however the MC3479
is only good for 0.35A so the motor you have selected will be slightly under driven by about 10%. Page 7 of the MC3479 datasheet shows how to calculate R2 and also to check the power dissipation in the device. My calculations are that R2 = (12-.7)/(350 x .86) = 37.5kohm which means the power dissipation is 2.8W, far higher than the device can tolerate without a decent heatsink. Since the original circuit has no heatsink, nor does it have any significant heat conducting traces on the board the stepper motor must be considerably smaller than the one you have selected. We can determine this from the resistor connected to pin 6 of the MC3479 and the supply voltage if known (or assumed), but I'll hazard a guess its below 200mA.

The stepper motor you have chosen can be used, but you'll need a good heatsink on the chip and a good ground plane on both sides of the PCB to help get the heat away...

Just goes to show that even copying a simple circuit can be difficult if not all the details are known....

[the0wn4g3]

The supply voltage is definitely DC. Says the transformer has an output of 8V and 500mA. I really have no idea of the part # for the diode...

Here's a pic with everything labeled: http://i4.photobucket.com/albums/y11...C02742copy.jpg

I'm slowly understanding how it's all working now. Still kinda hazy though...
So, with 8V R2 should be R2 = (8-.7)/(350 x .86) = 2.42kohm
That means power dissipated will be P = (8 x .068)+(2 x .35)(2+.8) = 1.38W
If I did that right, it should only reach around 97C, so I should be ok, right?

You are definitely right. I though I could order some parts, plug them into a breadboard, and have it working in no time. Never knew I'd have to learn so much about step motors! It's amazingly interesting how all of this works. I never thought there was so much going on in such simple electronics.

Thanks!

[irving2008]

Your calculations are almost right... (8-.7)/(350 x .86) = .0242 = 24.2k, you just got the decimal point out one place! I'd use 22k and 2.2k 2% tolerance resistors in series, if you can't find a 24k resistor.

So a 7.5v 0.35A motor will work.

If you reduce supply to 8v then R3 would be (8-6)/.01 = 200R (use 180R) although you could afford to run the 555 at 5v in which case R3 is (8-5)/.01 = 300R (use 270R) and the zener diode D1 would be a 5.1v device.

I note that the original uses a 2.2k resistor for R3 which suggests they are running the 555 and zener at 1/10 the current (1mA instead of 10mA) I suggested. That implies its a CMOS part (or not a 555 at all, but some sort of RTC chip designed to run on a battery). If you use the values I suggest you can use a CMOS or bipolar part interchangeably..

Not quite sure you're interpreting the banding on the resistors correctly.... 39k, 56k, 2.2k and 470R are all standard values.. the last band is the tolerance...so the 39k and 56k are 2%, 2.2k is 1% and 470R is 5%. The value of 470R for the LED dropper resistor suggests a supply voltage around 8volts. The 39K bias resistor therefore suggests a motor current of around 200mA as I suggested.

Well now you're good to go...

Still can't see how that original works tho, that 555 wiring is completely kooky..