controlling dc motor direction (help a newbie, please)

[[email protected]]

i have a 1.5-3vdc motor that i would like to turn on and off in
opposite directions using two microswitches. i'm new to electronics,
but from what i've learned so far, i think i want to use a 556 timer
and dpdt relay. striking a switch would turn on the 556 timer for x
seconds (5, i'm thinking), then the dpdt relay, then the motor. am i
right taking this direction?

also, would striking the other switch before the end of the process
cause a problem? i'm hoping that it wouldn't interrupt the motion, and
would like to know if i could have it be ignored by the circuit.

and, testing the motor speed, i've been using resistors to get my 9v
supply down to 1.5 and 3vdc. would i still go that route to control
motor speed, or is there another option?

and help would be appreciated. thanks

david

 

[Tom Biasi]

i have a 1.5-3vdc motor that i would like to turn on and off in
opposite directions using two microswitches. i'm new to electronics,
but from what i've learned so far, i think i want to use a 556 timer
and dpdt relay. striking a switch would turn on the 556 timer for x
seconds (5, i'm thinking), then the dpdt relay, then the motor. am i
right taking this direction?

also, would striking the other switch before the end of the process
cause a problem? i'm hoping that it wouldn't interrupt the motion, and
would like to know if i could have it be ignored by the circuit.

and, testing the motor speed, i've been using resistors to get my 9v
supply down to 1.5 and 3vdc. would i still go that route to control
motor speed, or is there another option?

and help would be appreciated. thanks

david

Hi David,

What do you really want to do?

You can reverse the motor with the switches and/or the relay, what do you
want to do with the timing?

BTW: Get yourself a 3 volt supply and forget about the resistors.

If you are looking for something more complicated Google PWM Motor control
and "H" Bridge.

Tom

 

[John Fields]

i have a 1.5-3vdc motor that i would like to turn on and off in
opposite directions using two microswitches.

---
Do you want the switches to be manually activated or do you want the
motor to actuate them alternately?
---

i'm new to electronics,
but from what i've learned so far, i think i want to use a 556 timer
and dpdt relay.

---
I can see using a DPDT relay to do the polarity switching, but what
purpose would the timer serve?
---

striking a switch would turn on the 556 timer for x
seconds (5, i'm thinking), then the dpdt relay, then the motor. am i
right taking this direction?

---
Dunno.

It's not really clear what you want to do.
---

also, would striking the other switch before the end of the process
cause a problem?

 

[Chris]

i have a 1.5-3vdc motor that i would like to turn on and off in
opposite directions using two microswitches. i'm new to electronics,
but from what i've learned so far, i think i want to use a 556 timer
and dpdt relay. striking a switch would turn on the 556 timer for x
seconds (5, i'm thinking), then the dpdt relay, then the motor. am i
right taking this direction?

also, would striking the other switch before the end of the process
cause a problem? i'm hoping that it wouldn't interrupt the motion, and
would like to know if i could have it be ignored by the circuit.

and, testing the motor speed, i've been using resistors to get my 9v
supply down to 1.5 and 3vdc. would i still go that route to control
motor speed, or is there another option?

and help would be appreciated. thanks

david

Hi, David. Your description is a little sketchy. I'm going to make a
few assumptions here, and you tell me where I'm wrong.

You've got a low voltage DC motor which you want to run at two speeds.
To do that, you want to apply two voltages: 1.5V and 3VDC.

Now, you want to run the motor both clockwise and counterclockwise. To
do this, you have two pushbuttons labelled CW and CCW. When you press
the CW button, you want the motor to go clockwise for 5 seconds. When
you press the CCW button, you want the motor to go counterclockwise for
5 seconds.

You forsee needing at least one 555 for this project and a DPDT relay,
but you're not sure what's going to happen if someone, say, presses the
CW button while the motor is going counterclockwise -- you don't want
to smoke anything. OK. Let's see if we can simplify this and make it
safe from accidental short circuits.

The first thing you could use is a specialty relay called an impulse or
latching relay. This is a relay that's got two coils and two internal
magnets. When you energize one of the relay coils, it moves the
armature toward that direction. A weak magnet helps keep the armature
on that side, whether the coil is energized or not, until the other
coil is energized.

These relays can be a little expensive, but if you're not switching too
much current in your motor (you're using a 9V battery, that indicates
your motor doesn't draw more than a few tenths of an amp), a surplus
telecom relay should do the job. You'll have to suppress any switching
arcing, but it is still an inexpensive solution. Jameco sells one that
can switch up to 2 amps as their P/N 206543CM for $3.79 ea.

For the rest of this, the circuit should be pretty simple. You can use
three "C" or "D" batteries in series to give you a 4.5V power supply
(you'll need the higher supply for the surplus relay) and an LM555.
Cut and paste this wiring diagram to M$ Notepad if your newsreader
doesn't have fixed font:
|
| VCC VCC
| + +
| | |
| .--o---o---o--. D V
| | | | | -
| D| | D| | VCC |
| - C| - C| + D V
| ^ C| ^ C| | -
| | C| | C| .-. VCC VCC |
| | | | | | | + + o-----. SW3
| | | | | | | | | | | Slow/
| | | | | '-' .---o---o--. .-. o Fast
| '--o o--' | | | R| | '\
| | | | | | | | \
| | o----|<-o---)----o | '-' o \
| | | | | | | | |
| | | | | | LM555 o--. o-----'
| o-------)----|<-' | | | | /|C
| | | o----o | | -------
|SW1 | SW2 | | | | | --- ---
|CW | CCW | | | | | NC/ | | NO
| | o | o o----o | | .----' '----.
| |=|> |=|> | | | | | _ |
| | o | o | | | | | / \ |
| | | --- | | | o---o( M )o---o
| === === --- '---o---o--' | | \_/ |
| GND GND | | NC | | |
| === === | '----. .----'
| GND GND | NO | |/ NC
| | --- ---
| | ------- VCC
| | C |/ +
| | | D |
| | o ->|---'
| | |
| | ___ |/
| '|___|-o-| TIP31
| 180 | |>
| .-. |
| 1K| | ===
| | | GND
| '-'
| |
| ===
| GND
|
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

The value of R is equal to the DC resistance of the DC motor. D is any
diode like the 1N4001 or 1N4002.

When you press either SW1 or SW2, you energize the appropriate relay
coil, and also trigger the 555 one shot (you seem to have R and C
values down). The motor will be on for your 5 seconds.

I'd guess this is pretty much complete. Now tell me how I got it
wrong.

Cheers
Chris

 

[Si Ballenger]

i have a 1.5-3vdc motor that i would like to turn on and off in
opposite directions using two microswitches. i'm new to electronics,
but from what i've learned so far, i think i want to use a 556 timer
and dpdt relay. striking a switch would turn on the 556 timer for x
seconds (5, i'm thinking), then the dpdt relay, then the motor. am i
right taking this direction?

also, would striking the other switch before the end of the process
cause a problem? i'm hoping that it wouldn't interrupt the motion, and
would like to know if i could have it be ignored by the circuit.

and, testing the motor speed, i've been using resistors to get my 9v
supply down to 1.5 and 3vdc. would i still go that route to control
motor speed, or is there another option?

and help would be appreciated. thanks

david

There are some simple setups at the bottom of the below page.

http://www.geocities.com/zoomkat/switch.htm

 

[Homer J Simpson]

i have a 1.5-3vdc motor that i would like to turn on and off in
opposite directions using two microswitches.

Why? Explain what you want it to do and why.

 

[Chris]

Hi, David. Your description is a little sketchy. I'm going to make a
few assumptions here, and you tell me where I'm wrong.

You've got a low voltage DC motor which you want to run at two speeds.
To do that, you want to apply two voltages: 1.5V and 3VDC.

Now, you want to run the motor both clockwise and counterclockwise. To
do this, you have two pushbuttons labelled CW and CCW. When you press
the CW button, you want the motor to go clockwise for 5 seconds. When
you press the CCW button, you want the motor to go counterclockwise for
5 seconds.

You forsee needing at least one 555 for this project and a DPDT relay,
but you're not sure what's going to happen if someone, say, presses the
CW button while the motor is going counterclockwise -- you don't want
to smoke anything. OK. Let's see if we can simplify this and make it
safe from accidental short circuits.

The first thing you could use is a specialty relay called an impulse or
latching relay. This is a relay that's got two coils and two internal
magnets. When you energize one of the relay coils, it moves the
armature toward that direction. A weak magnet helps keep the armature
on that side, whether the coil is energized or not, until the other
coil is energized.

These relays can be a little expensive, but if you're not switching too
much current in your motor (you're using a 9V battery, that indicates
your motor doesn't draw more than a few tenths of an amp), a surplus
telecom relay should do the job. You'll have to suppress any switching
arcing, but it is still an inexpensive solution. Jameco sells one that
can switch up to 2 amps as their P/N 206543CM for $3.79 ea.

For the rest of this, the circuit should be pretty simple. You can use
three "C" or "D" batteries in series to give you a 4.5V power supply
(you'll need the higher supply for the surplus relay) and an LM555.
Cut and paste this wiring diagram to M$ Notepad if your newsreader
doesn't have fixed font:
|
| VCC VCC
| + +
| | |
| .--o---o---o--. D V
| | | | | -
| D| | D| | VCC |
| - C| - C| + D V
| ^ C| ^ C| | -
| | C| | C| .-. VCC VCC |
| | | | | | | + + o-----. SW3
| | | | | | | | | | | Slow/
| | | | | '-' .---o---o--. .-. o Fast
| '--o o--' | | | R| | '\
| | | | | | | | \
| | o----|<-o---)----o | '-' o \
| | | | | | | | |
| | | | | | LM555 o--. o-----'
| o-------)----|<-' | | | | /|C
| | | o----o | | -------
|SW1 | SW2 | | | | | --- ---
|CW | CCW | | | | | NC/ | | NO
| | o | o o----o | | .----' '----.
| |=|> |=|> | | | | | _ |
| | o | o | | | | | / \ |
| | | --- | | | o---o( M )o---o
| === === --- '---o---o--' | | \_/ |
| GND GND | | NC | | |
| === === | '----. .----'
| GND GND | NO | |/ NC
| | --- ---
| | ------- VCC
| | C |/ +
| | | D |
| | o ->|---'
| | |
| | ___ |/
| '|___|-o-| TIP31
| 180 | |>
| .-. |
| 1K| | ===
| | | GND
| '-'
| |
| ===
| GND
|
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

The value of R is equal to the DC resistance of the DC motor. D is any
diode like the 1N4001 or 1N4002.

When you press either SW1 or SW2, you energize the appropriate relay
coil, and also trigger the 555 one shot (you seem to have R and C
values down). The motor will be on for your 5 seconds.

I'd guess this is pretty much complete. Now tell me how I got it
wrong.

Cheers
Chris

On second thought, a couple of minor tweaks. First, a standard 555
isn't too reliable at 4.5V, and as the battery voltage droops, it will
be a mess. Use a CMOS 555 instead. Second, the CMOS 555 can't crank
the current a standard 555 can, so it might be better to replace it
with a darlington NPN transistor. Also, in order to spare the relay
contacts (it is switching an inductive load), you might want to have
some kind of diode suppressor across the motor itself. You can either
use a P6KE12A (available at Jameco for $0.22 ea.) or just place a
1N4002 from each end of the motor to Vcc:
|
| VCC
| +
| |
| D V
| -
| \ | C
| -------
| --- ---
| NC |\ | NO
| .------' -------.
| | _ |
| | / \ |
| o------( M )------o
| | \_/ |
| | |
| | |
| | \ \ |
| o-----|<--->|-----o
| | \ \ | VCC
| '------. .------' +
| NO | \| NC |
| --- --- -
| ------- ^
| C | \ |
| o------------'
| From ___ |/
| LMC555 >-|___|-o-| TIP121
| 1K | |>
| .-. |
| 1K| | |
| | | ===
| '-' GND
| |
| ===
| GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Good luck with your project, and again, if this doesn't work for you,
let us know what you need.

Good luck
Chris

 

[[email protected]]

wow. let me first say thank you for all the responses and help. i'm
already gaining a better understanding of what i'm doing.

chris, you assumed right, except i don't want to vary the speed of the
motor. i'm leaning towards running it at 3vdc/0.7A, but i might go
with 1.5v (or somewhere in between). from my understanding of PWM, i
won't be needing one (it's for speed control, right?)

the motor (and direction) would be manually activated by pressing down
on a microswitch. as the microswitch won't be depressed throughout the
entire process (those 5 seconds), i need the timer to simply be
activated by the switch.

i haven't read many schematics, yet, but theese are making some sense.
i thought i would need a 556 timer, (one 555 for each switch, to send
different signals to the dpdt for cw/ccw).

i could probably say more, ask more questions, but i'm going to read
some more about timers.

thanks again!
david

 

[ehsjr]

i have a 1.5-3vdc motor that i would like to turn on and off in
opposite directions using two microswitches. i'm new to electronics,
but from what i've learned so far, i think i want to use a 556 timer
and dpdt relay. striking a switch would turn on the 556 timer for x
seconds (5, i'm thinking), then the dpdt relay, then the motor. am i
right taking this direction?

also, would striking the other switch before the end of the process
cause a problem? i'm hoping that it wouldn't interrupt the motion, and
would like to know if i could have it be ignored by the circuit.

and, testing the motor speed, i've been using resistors to get my 9v
supply down to 1.5 and 3vdc. would i still go that route to control
motor speed, or is there another option?

and help would be appreciated. thanks

david

View in courier font:


+3 ----+ +------+-----------------------------+
| | | |
|>| | +---+
Rrly-1 | |
n/o +---v n/o n/c v Drly-2
--------[Motor]--------
Drly-1 ^ n/c n/o ^---+
| |
+---+ |
| |
Gnd -------------+-----------------------------+



Rrly = Run relay - energize it when you want the motor to
run. It is a single pole relay

Drly = direction relay. Energize or de-energize to change
direction. It is a double pole, double throw relay and
contains 2 sets of contacts, labeled Drly-1 and Drly-2.

Both relays are shown in the enrgized position. +3 gets
to the top of the motor through the energized Rrly-1 and
Drly-1 n/o and common points. Gnd gets to the bottom of
the motor through the Drly-2 n/o and common point. When
you de-energize Drly, Gnd gets to the top of the motor
through the Drly-1 n/c and common point. + 3 gets to the
bottom of the motor through the Drly-2 n/c and common
point, and the Rrly-1 n/o and common point.

That is a basic circuit to give you independant control
of direction and whether the motor runs or not. It was not
clear what you have in mind as to timing and changing
direction. However, whatever you want to do is achievable
by controlling how/when/how long you energize the relays.

Ed

 

[Chris]

wow. let me first say thank you for all the responses and help. i'm
already gaining a better understanding of what i'm doing.

chris, you assumed right, except i don't want to vary the speed of the
motor. i'm leaning towards running it at 3vdc/0.7A, but i might go
with 1.5v (or somewhere in between). from my understanding of PWM, i
won't be needing one (it's for speed control, right?)

the motor (and direction) would be manually activated by pressing down
on a microswitch. as the microswitch won't be depressed throughout the
entire process (those 5 seconds), i need the timer to simply be
activated by the switch.

i haven't read many schematics, yet, but theese are making some sense.
i thought i would need a 556 timer, (one 555 for each switch, to send
different signals to the dpdt for cw/ccw).

i could probably say more, ask more questions, but i'm going to read
some more about timers.

thanks again!
david

Hi, David. I guess you're sold on the PWM concept. The series
resistor (switchable with SW3 in the above ASCII schematic) does waste
power. You can do that with a 556 like this (view in fixed font or M$
Notepad):
|
| .--------------------.
| | |
| VCC | VCC |
| + | + |
| | | | |
| .-. VCC VCC | .-. VCC |
| | | + + | | | + |
| | | 8| 4| | | | 8| 4|
| '-' .---o----o---. | '-' .---o----o---.
| | | RST | | | | RST | SW3
| >--)-----o | | o-----o |
| | | | | | | |
| | | |3 | .-. | |3 1.5V To
| o-----o o----o | | | o-----o Q1
| | | 555 | | | | | 555 | __--o->
| | | | | '-' | | .--o
| o-----o | | | | | | 3V
| | | | | o-----o | |
| | | | | | | | |
| | | | | o-----o | |
| | | | | | | | |
| --- '---o----o---' | --- '---o----o---' |
| --- 1| 5 | --- 1| 5 |
| | === | | === |
| === GND | === GND |
| GND | GND |
| '---------------------------'
|
|
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
Your switch gives you the option of the transistor being on all the
time (the 3V position, Q1 being driven by the 1st 555) or about half
the time (the 1.5V position, Q1 being driven by the second 555). You
use the RST pin on the 555 (pin 4) to only have the 2nd 555 on when the
1st one is on (being driven by SW1 or SW2).

Just insert this into the circuit where the one 555 is in the original
circuit, and remove the series resistor R and SW3 in the first circuit,
and you're good to go. You've reduced the current draw by not burning
up 1/3 the drive power with a series resistor when you want to drive
the motor with 1.5V.

I hope this is clear -- feel free to post again if it's not.

Either way, you've got a good working circuit that isn't too profligate
with power, and should work reliably for motors up to an amp (if you
use the 4.5V 3 "D" batteries and the darlington transistor. If you
would grace us with more information, we could possibly save one of
those "D" batteries -- like what's the current draw of the motor? But
this will also add to the circuit complexity (possibly leave the 2nd
555 on all the time, and use it as a charge pump to get a gate drive
voltage for a power MOSFET) and expense.

Sometimes it's best to just git 'r done. Your call.

Cheers
Chris

 

[Rich Grise]

i have a 1.5-3vdc motor that i would like to turn on and off in
opposite directions using two microswitches. i'm new to electronics,
but from what i've learned so far, i think i want to use a 556 timer
and dpdt relay. striking a switch would turn on the 556 timer for x
seconds (5, i'm thinking), then the dpdt relay, then the motor. am i
right taking this direction?

Pretty much, but I think you'll need more than just a 556 and one
relay. You'll need at least two - one for "on/off" and one for direction.
And each of them will need a driver transistor, snubber diode, and so on.

also, would striking the other switch before the end of the process
cause a problem? i'm hoping that it wouldn't interrupt the motion, and
would like to know if i could have it be ignored by the circuit.

Actually, it depends on what kind of circuit you build. What I envision
is the two sections of the 556, each being triggered by its own
microswitch, with the output of one going to the "reverse" relay and
the outputs of both "OR"ed together for the "ON" relay. In that case,
if it's going in reverse and you push the forward button, it will
start the forward timing cycle, so when the other timer times out,
the reversing relay will drop out, and try to instantly reverse the
motor. If it's going forward and you press the "reverse" button, it
will immediately try to reverse the motor.

So you'd need to come up with some kind of trigger lock-out while
the motor is running.

Good Luck!
Rich