Author Topic: amplify this circuit  (Read 2863 times)

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Offline blackbeardTopic starter

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amplify this circuit
« on: October 19, 2009, 06:38:12 AM »
hi guys. i'm trying to figure how to control my motors with as little pins as possible and without buying anything. i made this circuit using an inverter which i'd think would switch both inputs from high to ground but i'd like to hook up some stronger motors then that can supply. is there any way to amplify it? maybe an audio amplifier?

[img=http://img40.imageshack.us/img40/866/circuitj.th.png]
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Offline waltr

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Re: amplify this circuit
« Reply #1 on: October 19, 2009, 07:36:57 AM »
Not really sure what you are trying to do with that circuit. You have two outputs but no inputs!
Is the inverter just a 7404 like device? Where do the two outputs go?

A good way to switch motors on/off is with a MOSFET or even a bi-polar transistor. Look up H-bridges, you can use just a quarter of an H-bridge to switch a motor.
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Offline blackbeardTopic starter

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Re: amplify this circuit
« Reply #2 on: October 19, 2009, 07:55:02 AM »
oh sorry the +5v is the input (which happens to be +5v when high) and the outputs go to the terminals of the motor after being amplified. the inverter would be a 7404. basicly it switches output from high to low when the input is high and output B remains high when the input is high. when the input is low output B is grounded through the 1kohm resistor. i don't like H bridges since they take too much space. also having chips makes it look all cool since it looks more complicated even if it's not
« Last Edit: October 19, 2009, 07:59:37 AM by blackbeard »
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Offline waltr

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Re: amplify this circuit
« Reply #3 on: October 19, 2009, 10:01:42 AM »
If the motor only draws a few mA this could work. Think about the path the current takes in getting to and from the motor. When the input is LOW, output B is sourcing current to the motor and returning through the LOW input. Therefore the input needs to be able to sink the motor current.

A slightly better circuit would be to use an inverter and a buffer (or two inverters in series) with their inputs tied together. This way when one's output  is HIGH and other's is LOW. Microchip has a nice chip that does this well for small motors or as a MOSFET gate drive for larger motors. Part numbers are TC4467, TC4468 & TC4469. There is also  app note #906b on using these for an Stepper motor drive (think two DC motoers instead of the two coils in the stepper). These chips have a continuous output rating of 300mA.
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Offline Soeren

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Re: amplify this circuit
« Reply #4 on: October 19, 2009, 02:37:34 PM »
Hi,

Quote from: waltr on October 19, 2009, 10:01:42 AM
A slightly better circuit would be to use an inverter and a buffer (or two inverters in series) with their inputs tied together. This way when one's output  is HIGH and other's is LOW.
Won't do, as blackbeard doesn't want an H-bridge, which is what you create this way (trhe output of an inverter is a half bridge).

blackbeard <- did you consider how small integrated H-bridges can be?
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Offline blackbeardTopic starter

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Re: amplify this circuit
« Reply #5 on: October 20, 2009, 06:16:14 AM »
do tell. i just don't like having transistors poking out of my circuit if it's possible to avoid it. a bit of an obsessive compulsion.
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Offline Soeren

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Re: amplify this circuit
« Reply #6 on: October 20, 2009, 12:11:36 PM »
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Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Joker94

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Re: amplify this circuit
« Reply #7 on: October 21, 2009, 05:00:01 AM »
if you don't want transistors poking out of your circuit i think whats Soeren suggested and use a H-bridge IC is the best option.
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