# Designing a Simple Circuit - Ask for Feedback!

• daniel_i_l
In summary, the author is designing a simple circuit that includes a motor that can run for 5 seconds after the switch is turned off. He is using a power supply of 5.7 volts and 800 milliamps, and thinks that it might be better to connect the motor and coil circuits in parallel instead of in a series. He also suggests using a time delay circuit instead of a switch to keep the power on for the motor.

#### daniel_i_l

Gold Member
Hi,
I started to design a simple circuit and want to ask you what you think about it.
http://img152.imageshack.us/img152/8508/circuit.th.png [Broken]
Basically what I have is a motor that can be turned on with a switch and can run for 5 more seconds when the switched is turned off. The coil (electromagnet) can run for 5 seconds when the other switch is turned on. Since I don't need the timing to be precise I've decided to try the capacitor approach instead of a time delay relay since it's easier to implement (do you think that I should start with the relay system anyway?).
I'm using a power supply of 5.7V and 800mA. So R3 =V/I = 7.125 ~ 10ohm. R1*C1 = R2*C2 = 5 so:
R1 = R2 = 5Kohm and C1 = C2 = 1mF (10^-3).
Did I do that right? Am I missing something important here? Would it be better to connect the motor and coil circuits to R3 in parallel instead of in a series?
Thanks

Last edited by a moderator:
Are you expecting the motor to run at full speed for 5 seconds after the switch is opened? Is that realistic, given the way that a capacitor discharges?

I don't need it to run at full speed for 5 seconds, 1 or two will be enough - it'll be ok if it runs for more than 1 second and less than 5. Is that feasible with the capacitors?
Any other suggestions?
Thanks

daniel_i_l said:
I don't need it to run at full speed for 5 seconds, 1 or two will be enough - it'll be ok if it runs for more than 1 second and less than 5. Is that feasible with the capacitors?
Any other suggestions?
Thanks

You will not keep the motor running with the power off for anything like a few seconds. Instead, you should look into using a simple timing circuit to keep the power on for the motor for a couple seconds after the "off" switch is pressed.

It looks as if you are assuming your motor has negligible resistance compared with 10 ohms.
This seems unlikely.

I think it might be better to put the capacitance in series with the coil of a relay which has predictable resistance. The contacts of the relay could then be used to switch the motor on and off.

There is another consideration. If a relay closes completely (magnetically), it only takes a very small current to keep it closed. The leakage current of electrolytic capacitors might be enough to keep it closed. You also have to have some way for the capacitor to discharge and this path might also keep the relay from opening again.
You might have to put a bit of paper or insulation tape on the iron part of the relay that is attracted to the core of the coil, so that it can't close completely.

Another, better, way is to use electronics to provide a time delay.
A NE555 in monostable mode can switch a transistor to turn on a relay and switch on the motor.

## What is a simple circuit?

A simple circuit is a basic electrical circuit that includes a power source, a load (such as a light bulb or motor), and conductors (wires) connecting the power source to the load.

## What are the essential components needed to design a simple circuit?

The essential components needed for a simple circuit include a power source (such as a battery), conductors (wires), a switch, and a load (such as a light bulb or motor).

## What is the purpose of designing a simple circuit?

The purpose of designing a simple circuit is to create a pathway for electricity to flow from the power source to the load, which allows the load to function.

## What are some common mistakes to avoid when designing a simple circuit?

Some common mistakes when designing a simple circuit include using incorrect wire sizes, not properly connecting components, and not considering the voltage and current requirements of the load.

## Why is it important to ask for feedback when designing a simple circuit?

Asking for feedback when designing a simple circuit can help identify any potential issues or improvements that can be made to the circuit. It also allows for collaboration and learning from others' experiences and knowledge.