meassuring direct onto the sensor i get 0.14 volts without a magnet and it drops to 0.1 volts with a magnet

 

meassuring direct onto the sensor i get 0.14 volts without a magnet and it drops to 0.1 volts with a magnet

Something is clearly amiss. The output of the HE sensor should swing between around 12 volts (without a magnet) and near 0 volts (with a magnet).

Do you have another HE sensor you can try?

hgmjr

 

i have removed both diodes from the circuit and i have replaced the 100ohms resistor from the sensor the base to a 10K.
i am getting 0.11 volts on base and it drops to 0.01 when stopped over a magnet
the collector is 2.26 volts and does not move when a magnet is placed over the sensor and is saturating the power transistor

I found information that leads me to strongly suspect that the output transistor you are using is an NPN darlington. That would explain the 2.26 volt figure that you are getting for the voltage at the collector of the BC548.

hgmjr

 

i have very quickly connected up my last HE switch .
i get from the base 2.60 volts with out the magnet and 0.1volts on a magnet

 

i have very quickly connected up my last HE switch .
i get from the base 2.60 volts with out the magnet and 0.1volts on a magnet

Which base are you referring to?

hgmjr

 

sorry . the base direct on the sensor. i get 0.13 volts on the base of the transistor
may be i need new HE switch, which ones would be good for this project

 

sorry . the base direct on the sensor. i get 0.13 volts on the base of the transistor

Let me make sure I understand what you are telling me.

You use the phrase "base of the sensor". That is a bit unclear to me. Strictly speaking the hall effect sensor has an output not a base. Are you referring to the output of the hall effect sensor when you use this phrase?

hgmjr

 

yes i am .

 

So the output of the HE sensor is swinging between near 0 volts with a magnet and near 2.6 volts without a magnet. That sounds a bit low to me.

As an experiment can you disconnect anything that is connected to the output of the HE sensor and measure what the output swings under the no-load condition with and without a magnet?

hgmjr

 

You may need to temporarily disconnect the load on the power transistor so that it does not overheat.

hgmjr

 

i am getting those measurements with out a load. direction to the multimeter

 

Does the HE sensor you are now using have the A45 L label on it? Also, is this latest sensor brand new and never used? Could it have been damaged?

I wonder if the HE sensor now being used has been overstress some how.

hgmjr

 

the sensor is the same one as in the picture. with A45L on it.
the one a have just connected is new out of the box

 

You are powering the HE sensor from 12 volts, right?

hgmjr

 

yes from a small motor bike battery

 

OK. Another experiment is in order.

Using a 1K resistor connect it between the output of the HE sensor and the +12 volt supply. This will determine if is needs a pull up to swing the full range.

hgmjr

 

i now get on the out put of the sensor 12.5 volts drop to 0.16 volts on a magnet
i get 0.73 volts at the base of the transistor

 

That is more like what I would expect. For the time being I would keep the 1K pullup and move on.

Can you now proceed to connect up the 10K resistor to the output of the HE sensor and see how your overall circuit works?

hgmjr

 

i get 0.73 volts without a magnet and it drops to 0.16 volts on a magnet
sorry i have to go out i hope we can finish this off . thanking you very much for your help so far

 

Looking forward to getting you going.

We are very close indeed.

hgmjr