Modding electronics

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Prime
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Re: Modding electronics

Post by Prime »

Samaya,

this is what the current circuitry looks like.

Image



expressSCH does not have the LM350 so I used LM317's in my schematic. I may still use them in the final design.

The intention is that i have a fixed voltage from the transformer circuitry and then use the regulators with external pots to control the final output voltage.

Image

^^ I have added in my interpretation what I think you meant but I am not sure if its right and I do not understand about the second resistor R and main BJT or FET?

So, yes, I think I need help please :oops: , thanks.

Edit: changing the first image so its easier to read it next to the second image
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Re: Modding electronics

Post by Prime »

I need some help with some power circuitry on a autonomous vehicle i am conceptualising.

It's got an AVR micro controller which has got to read various inputs and give outputs based on these. That part is easy, in fact the basic code is written. I just have to adapt it to for a second motor.

What I am struggling with is the power circuitry. I have 2 unipolar stepper motors which say 4.3V and 1.2A. So that pretty much scraps the idea of using a darlinton array chip like a ULN2803A unless I buy some smaller motors.

I have a few bottles of powerfets such as IRFP350's and IRFP460's and some smaller ones somewhere in a bottle. If I use power fets, I assume I need to use drivers? Do I need to match the drivers to the FET's?

And should I go with Unipolar or Bipolar? Bipolar requires 2 H bridge's per motor.

Thanks.
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Re: Modding electronics

Post by Samaya »

Prime wrote:I need some help with some power circuitry on a autonomous vehicle i am conceptualising.

It's got an AVR micro controller which has got to read various inputs and give outputs based on these. That part is easy, in fact the basic code is written. I just have to adapt it to for a second motor.

What I am struggling with is the power circuitry. I have 2 unipolar stepper motors which say 4.3V and 1.2A. So that pretty much scraps the idea of using a darlinton array chip like a ULN2803A unless I buy some smaller motors.

I have a few bottles of powerfets such as IRFP350's and IRFP460's and some smaller ones somewhere in a bottle. If I use power fets, I assume I need to use drivers? Do I need to match the drivers to the FET's?

And should I go with Unipolar or Bipolar? Bipolar requires 2 H bridge's per motor.

Thanks.
AVR is AWESOME!!!!!

Anyway, its not always necesary to get FET drivers, it depends on the gate-to-source voltage against the Drain-to-source current. If you can get say 3A while at 3.3V then you can use it. BTW the IRFP350, according to IRF's website, has been divested - I can't even get a datasheet from their site. I like using the IRLZ44NS from IRF. It has a 47A continuous (pusled 160A) drain current and for a bonus, you can get about 20A from a 3.3V input. Overkill I know but I like overkill with FET's...

It's been a while since I have used a stepper motor. How many bits/lines/coils is used to control your steppers? If I remember correctly, steppers do not require h-bridges for direction changes (I cant remember very well now) so you would probably be fine if you use single transistors to change line voltages.

Anyway, good luck with your project.

S
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Re: Modding electronics

Post by Prime »

Samaya wrote:AVR is AWESOME!!!!!
Now that I am getting the hang of it, totally :mrgreen:
Samaya wrote:Anyway, its not always necesary to get FET drivers, it depends on the gate-to-source voltage against the Drain-to-source current. If you can get say 3A while at 3.3V then you can use it. BTW the IRFP350, according to IRF's website, has been divested - I can't even get a datasheet from their site. I like using the IRLZ44NS from IRF. It has a 47A continuous (pusled 160A) drain current and for a bonus, you can get about 20A from a 3.3V input. Overkill I know but I like overkill with FET's...

It's been a while since I have used a stepper motor. How many bits/lines/coils is used to control your steppers? If I remember correctly, steppers do not require h-bridges for direction changes (I cant remember very well now) so you would probably be fine if you use single transistors to change line voltages.

Anyway, good luck with your project.

S
Firstly, about the steppers. 4 coils/bits. Mine have 6 lines. 2 of the wires are commons.

http://www.solarbotics.net/library/pdfl ... torbas.pdf

6 wire motors are unipolar. this means that all you need to do to drive them is hook the commons to power and sequentially drive the 4 other wires.
But if you want to drive in a bipolar config, you ignore the commons and have to forward and reverse the polarities across two coils. It's supposed to give more torque but you need an Hbidge to do this. The only thing affecting the direction of rotation is the sequence you use to switch the coils on and off with.

I have the datasheet for the IRFP350's and they can handle 16A cont and 46A pulsed. And RDS = 0.3 ohms with a max threshold voltage of 4 volts. My microcontroller puts out 5 volts per pin I think.

But the ones you mnetioned would be better because their RDS value is 0.022 ohms with a threshold voltage of 1-2 volts. I trying to work out what my DS voltage and current needs to be to put my fets in the right region. what do I put in for KN (conductivity)? I know I need a DS voltage of atleast 3v to achieve saturation (VDS(sat) = VGS - VTH) My GS Voltage is 5 volts and according to the datasheet for the IRLZ44N the threshold is 1-2 volts.

edit: RD = 3 ohms which is a coil on my motors :shock:
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Re: Modding electronics

Post by Prime »

Anyone figured out how to get a old roland plotter to work on XP or vista/7?

Someone at varsity donated one to me... but I can't find drivers. Eagle will generate a HPGL file - can i just stick it into a terminal program?
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Re: Modding electronics

Post by Samaya »

You have difficult questions on a monday morning. I don't think you would be able to use the terminal program like that. But try and see what happens. Otherwise get yourself Docklight (http://www.docklight.de). IT IS FANTASTIC. You monitor your serie port and on certain marked strings you can have a command of your own sent back to the unit. There is also a scripting version available. It is really good
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Prime
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Re: Modding electronics

Post by Prime »

much easier:
[]type whatever.hpgl > LPT2: [] into your command prompt and away she goes...

:)

now I need a decent pen, the ones in the lab are stuffed!
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