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Electronic Switch

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Monkeymon

New Member
hi
i have some problem about making a electronic switch.
im currently doing a project base on a 68HC11 micro-controller board.
im trying to have the board to control another board by using the output pins of the board as a switch.
when the pin is high its 3.3v and low is 0.9v. and when the pin is high, i want it to be connect and low to disconnect.
i have a switch using a 2n222 npn transitor but it seem to activate even when the pin is low.
is there any other of making a electronic switch ??
i have draw the circuit of the switch i have do but dun seem to work ..
 

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Klaus

New Member
OK, first let me say that I do not have the specs for a 2n222 so my answer is more in general. You do not show what supply voltage the transistor gets but it should have a load resistor, either in the collector or the emitter lead.

Next, try to use a lower value than the 1k5 resistor at the base (or a higher resistance than the 4k7 resistor). Measure the base to emitter voltage with a digital volt meter, it should be less then 0.5V for the transistor to turn off.
 

Monkeymon

New Member
Klaus said:
OK, first let me say that I do not have the specs for a 2n222 so my answer is more in general. You do not show what supply voltage the transistor gets but it should have a load resistor, either in the collector or the emitter lead.

Next, try to use a lower value than the 1k5 resistor at the base (or a higher resistance than the 4k7 resistor). Measure the base to emitter voltage with a digital volt meter, it should be less then 0.5V for the transistor to turn off.

ok i will try using a lower resistor value at the base.
is there any possible way to use a relay ????
 

Optikon

New Member
Monkeymon said:
Klaus said:
OK, first let me say that I do not have the specs for a 2n222 so my answer is more in general. You do not show what supply voltage the transistor gets but it should have a load resistor, either in the collector or the emitter lead.

Next, try to use a lower value than the 1k5 resistor at the base (or a higher resistance than the 4k7 resistor). Measure the base to emitter voltage with a digital volt meter, it should be less then 0.5V for the transistor to turn off.

ok i will try using a lower resistor value at the base.
is there any possible way to use a relay ????

You do not show the load your switch is connected to. You do not want your transistor shorting your Vcc to ground. Also verify that it is the emitter lead that is going to ground. You should measure about 0.65 Volts from base to emitter when the transistor is just turning on (approximately) - verify that is so.

And yes it is possible to use a relay - whether or not you need to do that depends on your load requirements. If you do use a relay, you will use more parts and they will likely be larger in physical size.
 

Monkeymon

New Member
i have draw the actual connection of my board....

can help me see what have i done wrong in the connection....
 

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Russlk

New Member
The 2N222 emitter should return to ground, not -9 volts. If the IC requires a negative voltage to be off, then use a 2N2907 PNP transistor with the emitter returned to +5 volts.
 

Monkeymon

New Member
Russlk said:
The 2N222 emitter should return to ground, not -9 volts. If the IC requires a negative voltage to be off, then use a 2N2907 PNP transistor with the emitter returned to +5 volts.

which means that the emitter side of the transistor should return to ground... i will try that and if it work....

i have some qns on the relay thing...
if i have a relay that work on 5v but i only have 3v which is not enough to activate it.
can i add in another voltage source which is 2v to add it up to 5v ??
and if i remove the 2v supply will the relay be d/c ??
 

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aryajur

New Member
If you add the 2 volts in parallel as I suppose you are trying to do, u will be effectively loading the 3 volt supply and may damage it too. The 2 volts should appear in series witht the 3 volt supply.
 

Sebi

Active Member
With a transistor switch You can choose the relay voltage independently from proc voltage.
 

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Monkeymon

New Member
aryajur said:
If you add the 2 volts in parallel as I suppose you are trying to do, u will be effectively loading the 3 volt supply and may damage it too. The 2 volts should appear in series witht the 3 volt supply.

how should i do that ???
can i do it by connecting out source to the base of the transistor and other to the collecter of the transistor ??
 
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