Welcome to the North American Subaru Impreza Owners Club Monday July 28, 2014
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Here you can view your subscribed threads, work with private messages and edit your profile and preferences Home Registration is free! Visit the NASIOC Store NASIOC Rules Search Find other members Frequently Asked Questions Calendar Archive NASIOC Upgrade Garage Logout
Go Back   NASIOC > NASIOC Technical > Electrical & Lighting

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads.
Reply
 
Thread Tools Display Modes
Old 05-13-2008, 06:54 PM   #1
efmd3
Scooby Specialist
 
Member#: 120985
Join Date: Jul 2006
Chapter/Region: South East
Location: Birmingham, AL
Vehicle:
2002 Impreza WRX
Midnight Black Pearl

Default Circuit Design help.

I'm trying to build a controller that can take a 0-5V signal and use it to control a 12V motor.

Ideally, I'd like there to be a gain curve where
0V=0V
>~3V=12

but the easiest way to do this would be a simple on off switch controlled by the Input voltage.

with my limited electrical knowledge, I think I am looking for a transistor.

if I wired a variable resistor to the transistor, I should be able to adjust the threshold at which the 12V circuit is opened...right?
* Registered users of the site do not see these ads.
efmd3 is offline   Reply With Quote
Old 05-14-2008, 06:08 PM   #2
growling_boxer
Scooby Specialist
 
Member#: 165744
Join Date: Dec 2007
Chapter/Region: Tri-State
Location: Eastern PA
Vehicle:
2000 LGT
2007 STi

Default

a potentiometer could certainly be used to adjust the threshold voltage for your transistor if you want to use it as a switch. if the 0-5V signal is variable, and not just on-off, i think you want to use an op amp to step the signal up to 0-12V.
growling_boxer is offline   Reply With Quote
Old 05-15-2008, 02:00 PM   #3
Mike Costin
Scooby Specialist
 
Member#: 131787
Join Date: Nov 2006
Chapter/Region: Tri-State
Location: Sandy Hook
Vehicle:
06 STI,OB,OME XJs
Merkur Junkyard

Default

If you need linear gain between 0.7V and 3V then you could use an op amp like the previous poster said. I wouldn't consider a single transistor setup, it would be a pain to convert the input into a small signal and keep the BJT in its linear region. None of this really matters because you shouldn't drive a DC motor with these circuits!

First, what are the motor specs and what are you doing with it?

At the minimum you will need a half or full H-bridge, these come in IC form like the L298. The half H-bridge is for a single direction only. These usually accept 0VDC low, 5VDC high (TTL on at 2-3V) so it's perfect for your application. Some H-bridge ICs come with back-EMF protection, some like the L298 don't and you'll need to use additional diode junctions for that.

The rest of the circuit depends on how much speed control you need. If it's "not much" and you can deal with different motor speeds and minor oscillations then you can just use a potentiometer in series with the motor. If this is going in a vehicle remember to drip candle wax over the pot so it doesn't spin from vibration.

If you need precise speed control then you will need to do Pulse-Width-Modulation with a digital microprocessor like a PIC.

Remember to choose components that can dissipate enough heat for your application.
Mike Costin is offline   Reply With Quote
Old 05-15-2008, 02:21 PM   #4
growling_boxer
Scooby Specialist
 
Member#: 165744
Join Date: Dec 2007
Chapter/Region: Tri-State
Location: Eastern PA
Vehicle:
2000 LGT
2007 STi

Default

After re-reading the first post, it sounds like you don't want speed control over the motor by varying the voltage. you simply want on-off control. in that case, you don't need the op-amp.

Quote:
Originally Posted by Mike Costin View Post
First, what are the motor specs and what are you doing with it?
this really should have come first...

Quote:
Originally Posted by Mike Costin View Post
I wouldn't consider a single transistor setup, it would be a pain to convert the input into a small signal and keep the BJT in its linear region. None of this really matters because you shouldn't drive a DC motor with these circuits!
i don't think he wants to use the BJT in its linear region, since i think he wants on-off. so the OP should probably be using MOSFETs appropriately sized for the power necessary, possibly just using the FET to control a relay if there is that much power running through the motor signal.

Quote:
Originally Posted by Mike Costin View Post
Remember to choose components that can dissipate enough heat for your application.
this may also require some sort of a heat sink if your driving the motor directly through a transistor. also make sure you are using parts that are automotive or military grade when there is the option--possibly with FETs (i forget, since it's been a while since i had to source my own parts), and definitely with any ICs.
growling_boxer is offline   Reply With Quote
Old 05-15-2008, 03:00 PM   #5
rkramer
Scooby Guru
 
Member#: 118209
Join Date: Jun 2006
Chapter/Region: MWSOC
Location: North Dakota
Vehicle:
2002 WRX Sedan

Default

wow, let a bunch of smart guys design anything, and simplicity goes straight out the window!

since you didn't specify, i'm assuming that is a good 5 volts, not a chip logic level output? if so, it isn't hard to find a 5 volt relay that will kick on around 3 volts.
rkramer is offline   Reply With Quote
Old 05-15-2008, 03:11 PM   #6
growling_boxer
Scooby Specialist
 
Member#: 165744
Join Date: Dec 2007
Chapter/Region: Tri-State
Location: Eastern PA
Vehicle:
2000 LGT
2007 STi

Default

if he doesn't need the power-handling of a relay, it could be a costly option, especially if it needs to handle being in the engine compartment.
growling_boxer is offline   Reply With Quote
Old 05-17-2008, 04:55 PM   #7
efmd3
Scooby Specialist
 
Member#: 120985
Join Date: Jul 2006
Chapter/Region: South East
Location: Birmingham, AL
Vehicle:
2002 Impreza WRX
Midnight Black Pearl

Default

turns out i don't need it, which is a bummer because it would have been a killer fun project.

I learned A LOT about transistors though

thanks for all your help guys
efmd3 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Circuit design question quantum Off-Topic 16 02-25-2009 12:13 PM
Electrical circuit design question (OT EE's, come in) cucamelsmd15 Off-Topic 38 02-12-2009 10:20 AM
Circuit design techie needed - MIL eliminator design SubaruStu General Community 18 05-11-2002 05:10 PM
Circuit Design People - Wayne? Need Help. EBC Monkey webkris New England Impreza Club Forum -- NESIC 63 01-14-2002 03:13 AM
1 amp keyed circuit?? Need help Ken Levin Factory 2.0L Turbo Powertrain 4 01-07-2002 08:58 PM


All times are GMT -4. The time now is 11:52 AM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2014 Axivo Inc.
Copyright ©1999 - 2014, North American Subaru Impreza Owners Club, Inc.