Help with a momentary circuit

Thread Starter

stf5060

Joined Oct 5, 2011
11
Hi,

I have never really built anything too complicated from scratch, only followed pre-made guides and I'm looking for some help. Basically I bought a 12V 15RPM motor that I will have hooked up to a remote activated outlet plug. I want to make a circuit that will, when the power is activated from the plug, turn the motor on for somewhere between 1-5 seconds (I haven't decided yet) and then turn it off. Can someone help me figure out a method for doing this? Your help is much appreciated. Thanks
 

THE_RB

Joined Feb 11, 2008
5,438
This forum (and google) are full of "555 timer circuits" that should do what you need.

The 555 timer is a small easy to use IC that lets you make a time delay.

The 555 can drive a relay or transistor that controls the motor power. So try "555 timer with relay" or "555 timer control DC motor" or similar searches. :)
 

Georacer

Joined Nov 25, 2009
5,182
Don't forget that this site doesn't allow circuits connected directly to the mains.
If you post any circuits, make sure they are electrically isolated from the wall plug through a 1:1 transformer.
 

KMoffett

Joined Dec 19, 2007
2,830
For remote activation of a power outlet, look into X10 modules. Off the shelf and safe. No need to mess with power line interfacing.

Google:X10

Depending on how much current the motor draws, you can power the motor and a 555 timer circuit from a 12V wall wart plugged into an X10 receiver.

Ken
 

Thread Starter

stf5060

Joined Oct 5, 2011
11
Thanks for the link. So I will try and build the monostable circuit. The only problem is I was planning on using 24v .3 amps, which I see is too much for a 555 timer. Would this work to downgrade the voltage? http://www.ebay.com/itm/5-x-L7812-7812-Voltage-Regulator-12V-1-5A-Ham-Kit-/140614607735?pt=LH_DefaultDomain_0&hash=item20bd48a377

So I'm assuming if I drop the voltage to 12v the current is doubled to .6 amps, correct? Now what can I use at the end to bring the voltage back up to 24v? And I'm having trouble finding a 100k resistor like the one in the diagram that is suitable for 24v .3 amps (~8watts), anyone have any ideas? Thanks for the help guys
 

Thread Starter

stf5060

Joined Oct 5, 2011
11
I forgot to mention I need to make 3 of these circuits. 1 for the motor which is 12v and the other 2 for actuating solenoid valves at 24v
 

KMoffett

Joined Dec 19, 2007
2,830
OK, how much current does the 12V motor draw maximum, in the start/stalled condition? How much current does each of the solenoid valves draw? Are there any other things attached to this we will need to take into account.

The devil's in the details!

Ken
 

Thread Starter

stf5060

Joined Oct 5, 2011
11
I'm waiting on the specs for the 12v motor, but I'm not as concerned about that. The solenoids will be operating on 24v 0.3Amps. There won't be anything else attached to the circuit. I just simply need them to open for a short amount of time, and then shut, and the circuit to not retrigger them to open. And then power will be cut from the circuit after a short amount of time
 

Thread Starter

stf5060

Joined Oct 5, 2011
11
Wow! Thanks so much for the diagram, much appreciated! I just have a few questions if you don't mind. For the 24v circuit, you used a 1N4742A zener diode, but it says its only rated for 1W, isn't that too small? Doesn't everything have to be rated for like ~8W? And Which of the capacitors/resistors do I have to adjust to adjust to output time? Could you recommend a good site to order all or most of this stuff? Instead of hunting around for each part. Thanks again for all your help!
 

KMoffett

Joined Dec 19, 2007
2,830
The zener only supplies current to the timer circuit that draws very little, so 1W should be sufficient. R3 is a potentiometer used as a variable resistor to adjust the time. I'll take a look at the components and give you a vendor.

Ken
 

SgtWookie

Joined Jul 17, 2007
22,210
Ken,
Shouldn't use a Zener like that. You need the circuit voltage regulated, not the drop from 24v down to the timer voltage. You take a chance that a spike will zap the circuit; and you're using a CMOS timer and a MOSFET for a driver. Odds are that one spike will kill them both.
 

Thread Starter

stf5060

Joined Oct 5, 2011
11
...So, what would you suggest? And since the zener is only rated for 1W does that mean I can use capacitors and resistors for 1W as well? I was under the impression I needed something that parts that could support about 8W for everything. Thanks again for all the help guys
 

SgtWookie

Joined Jul 17, 2007
22,210
Steven,
In the right-hand schematic, D2 and R1 need to be exchanged. R1 needs to be reduced to allow between 10-20mA current to flow through it. That's 600 to 1.2k Ohms.

Also, 0.1uF and 1uF or larger caps need to be connected across the Vcc and GND terminals of both 555 IC's.
 
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