Beginner need help with hall sensor and transistor switch

[cloakinghalk]

I am working with a friend trying to complete a project and we need to send a square wave from 0-5 volts to a camera continuously after a hall sensor is triggered. I know nothing about transistors and I am having a hard time trying to figure this out. The power supply is 5volts and the hall sensor ranges from .6 volts normally to 1.2 volts when triggered. I am thinking that I need a transistor as a switch to turn on when 1.2 volts. Then another type of gate to provide power there after and then maybe a 555 timer to create the square wave from 0-5. Does anyone know how to do this?

 

[MikeMl]

Why not just get a **broken link removed**.

 

[Dr_Doggy]

hook the out of the hall sensor to the base of a transistor, and you can use that to enable a 555 timer,

put a flipflop in there too if you want it to latch

 

[cloakinghalk]

The logic hall sensor isn't water proof. The sensor is going to be a foot under water. I'm using a cam sensor from a gmc car because its water proof. I tried to use a transistor but I can only get it to work in a basic circuit. When I put the sensor to the base of the transistor it just stays on all the time. I have been trying to look at LDR circuits to get some type of basis but it still just stays on all the time.

 

[Dr_Doggy]

use a npn transistor, if it wont turn off put a resistor in between, use a pot to adjust it since value will change based on gain on transistor

 

[ronv]

Hall

There are a few unanswered questions:
Do the pulses turn off when the Hall turns off? This circuit does
What frequency of pulses? I just picked one
Note the first pulse from the 555 is longer than the rest. This is how it comes out of reset. Is that ok?

 

[MikeMl]

Here is how I would do it. Set the 5K Pot about 3/4 of the way from the bottom, until the voltage at "RC" pulls all the way to ground. The time-constant of R1*C1 determines how long the 555 stays triggered after the Hall pulse goes low. Useful range of R1 is 10K to 10meg.

 

[cloakinghalk]

I believe both of your schematics will work. The frequency I believe should be around 10hrtz but I'm not positive. I'll have to go and check the manual for the camera. I will try both out. What transistor should I get for MikeML and what op-amp for Ronv?

 

[MikeMl]

Any small signal NPN will work: 2n3904, 2N2222, 2N4124, 2N4401, and about a 1000 others.

 

[cloakinghalk]

Ok thanks, Ill get it now and try it out

 

[ronv]

Clicker

The LM393 or LM319 are probably the easiest to find.
Schematic with 10 sec. timer attached.

 

[cloakinghalk]

Thanks, Ron and Mike, I didn't try Ron's but Mikes works perfect. It triggers the camera perfectly. Thanks a lot for the help.