Help with an amplifying circuit!

Hi,
I'm looking to build a laser based burglar alarm for a school project. I already have a laser and a phototransistor in mind, however i do not know how to design a circuit that will amplify the current from the phototransistor which will then eventually go to the siren/alarm itself. Please help! Thanks.

**broken link removed**

you need something called a transimpedance amplifier.

If you search on google for transimpedance you should get the basic jist of what is needed.

At the end of the day it is just an op-amp circuit just the feedback is chosen based on teh sensitivity of yr photo device. Because of that no specific cct can be provided without knowing what device you are using. But search and you should get the idea

You did not mention the generic of your sensor/phototransistor. If this is an NPN phototransistor check the max Vceo say if this is 30V. you can probably use a lower voltage(eg. 12/24vdc) as pull up, such that when it senses your laser beam it causes your phototransistor into saturation driving a relay coil and the contact of which will switch your sirens.goodluck

ray madayag said:

You did not mention the generic of your sensor/phototransistor. If this is an NPN phototransistor check the max Vceo say if this is 30V. you can probably use a lower voltage(eg. 12/24vdc) as pull up, such that when it senses your laser beam it causes your phototransistor into saturation driving a relay coil and the contact of which will switch your sirens.goodluck

Click to expand...

You will need a diode across the relay coil to protect the transistor from the back EMF when the transistor turns off. Connect the anode to the transistor's collector.

The circuit described is simple but a bit crude as assumes that the photo transistor has sufficient gain to drive a relay.

Len

laser

hi,

try this site, **broken link removed**