# Solenoid Alarm Clock in Series -- Voltage Problems –Amplification

Discussion in 'General Electronics Discussion' started by EDDGroupAlpha, May 12, 2013.

1. ### EDDGroupAlpha

1
0
May 12, 2013
We are trying to put a solenoid into series with an alarm clock, in order to go off when the voltage jumps from the alarm going off. However, the voltage varies too much and does not reach a high enough current to power the solenoid.
Solenoid
Alarm Clock
We used a multi-meter to measure out the range and goes at the highest to around 1.5V. The voltage varies with the pitch of the alarm. When the alarm is not going off, the solenoid is not active. We are actually on an ac voltage, but the Alarm Clock is converting the ac current.

We are looking into this, but it is more than a little confusing. We were thinking that we could amplify the signal, and then use a diode, to keep it from exceeding the max the Solenoid can take (5V).

Transistor as An Amplifier (links)

http://www.st-andrews.ac.uk/~www_pa/Sco ... page1.html

The datasheet for the solenoid can be found here.

https://www.sparkfun.com/products/11015

***Any information on how we could attempt to fix this would be appreciated and all used information will be cited along with relevant posts. ***

2. ### duke37

5,364
771
Jan 9, 2011
The St Andrews University link did not work for me.
The sparkfun link was not too clear but I think the solenoid has a resistance of 19 ohms.
The power is therefore not minimal.

You will need to detect when the alarm clock goes off and then use it to switch a power supply to the solenoid.

A mains clock may not have an isolating transformer so could be dangerous if opened.
Detection of the clock current with a Hall effect device or a current transformer could be done without opening the clock.

3. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
652
May 8, 2012
This statement makes me suspicious that the voltage you're measuring is not DC but rather pulsating DC (audio frequency) driving a Piezo.

Chris