Design Circuit Help

Hello
I am looking for a Small circuit that will run a motor for a set amount of time. Here are my circuit requirements:

1. Using a Reed switch, closed with a magnet, Off position, Circuit
activated by removing magnet from Reed Switch and Reed Switch
contacts closed.
OR
If Reed switch operation is reversed by magnet, N.O then closed with
NO magnet. Either is o.k with me.

2. NE555P with a Run time of 30 Seconds to 40 seconds. Please show
Resistor, Capacitor Calculation for Run Time for further use.
3. At end of run time motor shuts off, unit is dead
4. To reset circuit, Close Reed OR Open switch with magnet
5. Motor is a D.C Brushed motor, low Current, 3-5v pager type motor

I hope someone can help me with this.

Thanks In advance for your help.

George

I'll be glad to help you. First the circuit for the time you wish may not work with the NE555P because of the large value of capacitor and low value resistors. The leakage current of the capacitor may not allow the 555 to
work correctly. I would recommend the CMOS version, such as TS555CN.
I will draw you a circuit with values. I need to know the battery voltage.
I plan to use the reed switch closure to activate the time and, when the time is up the motor will be turned off.

Hello Again

First, Thanks to the admin. for moving my post to the proper section.

Secondly, Thank You k7elp60 for your help.

The battery, I am honestly NOT sure of because it is to power a small electric torpedo that will be in the water. From what I`ve seen on the market the voltage range is from 12v down to approx. 3.4v. My choice of the NE555P is because it is small and I have lots of them in stock. I plan to wire the parts to the pins of the 555 so as to make it as small as possible to fit inside. Not sure how your 555 would hold up to water and any possible static environment.
George

555 chips are all the same size.

No electronics hold up to water, because electricity conducts through wet things. Seal it or keep it away from water.

george0039 said:

Hello Again

First, Thanks to the admin. for moving my post to the proper section.

Secondly, Thank You k7elp60 for your help.

The battery, I am honestly NOT sure of because it is to power a small electric torpedo that will be in the water. From what I`ve seen on the market the voltage range is from 12v down to approx. 3.4v. My choice of the NE555P is because it is small and I have lots of them in stock. I plan to wire the parts to the pins of the 555 so as to make it as small as possible to fit inside. Not sure how your 555 would hold up to water and any possible static environment.
George

Click to expand...

I see two problems that need to be addressed. 1. The NE555p will not work below 5V and 2. since you are using a pager motor you will have to limit the voltage to it if the battery is higher than the specified voltage. I assume you plan to build the circuitry in some type of container that will be waterproof.

Put torpedo in find box, this page, upper right, & look for 10 sec, timer, OP trout, making a scale electric torpedo.

k7elp60 said:

I see two problems that need to be addressed. 1. The NE555p will not work below 5V and 2. since you are using a pager motor you will have to limit the voltage to it if the battery is higher than the specified voltage. I assume you plan to build the circuitry in some type of container that will be waterproof.

Click to expand...

Hello Again

Thanks for ALL the replies. Yes I know water and electronics don`t mix. It will be in a small water tight section.

As for the motor, the pager motor is one option, I also have hi rpm helicopter motors. As for the battery, I have one for testing, a 23A-12v alkaline and can find some others at a lower level as long as I know what to look for. The circuit is what I would like to see and if I need to get the other 555 version, then I will.

Thanks for the search tips, will be going through them shortly.

Only found a reference for an Ultra small timer from a magazine BUT unable to find schematic of it.

I am Still willing to try any provided circuit for my need. Please let me know what the Min. to Max. voltage of the 555 is and what is needed to run the motor from it safely BUT space is a factor. IT all will be in a dry section.

George

georg0039
Here is two schematics. Schematic A is if the motor only needs about 200mA. Schematic B will supply up to 1A for the motor. You can build the timer with the 3.0M and 10uF capacitor to check the timing of about 33 seconds. If you want to test the time without the motor connect a LED - lead to ground, + lead to one lead of a 1K resistor. The other lead of the resistor to pin 3 of the 555. Use 6V,9V or 12V as the power If the LED comes on for about 33 seconds and then goes off all is well.
The schematics are posted

Hello k7elp60

First, Thank You for your help. I will focus my work on circuit B. I have a couple question though. I see Pin 5 has a connection but goes no where? Also what is the Min. and Max. Power that this circuit can run on? Just to be battery safe.

Also I see that the IC is a NE555, no letters at the end? Could I use my NE555P for this work?

Thanks Again for your Time and Help. There will be a bit a delay before I can get to this trial circuit, I`m in the middle of another project in an other field.

George

george0039 said:

Hello k7elp60

First, Thank You for your help. I will focus my work on circuit B. I have a couple question though. I see Pin 5 has a connection but goes no where? Also what is the Min. and Max. Power that this circuit can run on? Just to be battery safe.

Also I see that the IC is a NE555, no letters at the end? Could I use my NE555P for this work?

Thanks Again for your Time and Help. There will be a bit a delay before I can get to this trial circuit, I`m in the middle of another project in an other field.

George

Click to expand...

You can use the NE555P, but if it does not time out in a reasonable time it means the NE555P will not work do to capacitor leakage current. The current can be up to 5A with a heat sink on the transistor. Here again power = volts x amps so at 12V with a emitter to collector volts of 2 the power would be 10W. Pin 5 is unused and is left open.