## Need to make a schematic circuit

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Moderator: Benj

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Joined: Tue May 12, 2015 10:00 am
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### Need to make a schematic circuit

OK guys this is what i wanna do :
i'm wanna command a 12 volt relay with an LED (EB004)
the LED "D2" when it's lightened it's 5V so i have to convert 5V TO 12V and send it to RELAY so the relay is actually commanded by the LED "D2"
should i use a REGULATOR 7812 to convert the voltage ? will it work ? the picture below will explain what i want but it's not circuit i want how can i modifie it ?
PLEAZE HELP ME i have two days to find the solution
I'LL BE REALLY GREATFUL IF YOU REPLY TO ME WITH THE PICTURE OF THE CIRCUIT I WANT
Attachments
Sans titre.png
i want to change the circuit on the right so that the relay have it's voltage from the converted 5V to 12V

kersing
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### Re: Need to make a schematic circuit

What is wrong with the diagram you posted? The transistor/diode combination will translate the input voltage for you. Just make sure to connect the grounds and apply 12 volt to pin 2 of J3.

“Integrity is doing the right thing, even when no one is watching.”

― C.S. Lewis

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Joined: Tue May 12, 2015 10:00 am
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### Re: Need to make a schematic circuit

the problem is within the 12V power supply i have to use the multiprogrammer EB006 power supply "14v" which i'm afraid it will destroy the relay board or destroy the multiprogrammer in a worst case issue
so i have to convert the power supply from 5V of the LED board to 12V
by the way i already tested the relay board (picture on my previous post) and it didn't work i think i put the wrong resistance value for transistor base (BC337) so what is the right current value for the transistor base to ensure PROPER SATURATION and the RESISTANCE VALUE that should work with it ?
and thank you

medelec35
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### Re: Need to make a schematic circuit

If using a 2K2 resistor then maximum base current is 5/2.2E3 = 2.3mA
The 12V supply can be connected to J3.
GND should be via pin 9 of 9Way D type connector.

If relay board is not working then check 5V is going into R1 from pin 3 of 9way connector (measure with -ve lead of meter connected to gnd)
If it is then check between collector and gnd.
with 5V going into R1and assuming 12V supply the voltages are approx:
Between
C & E = 0.1 to 0.2V
B & E = 0.6 - 0.9V
Across Relay = 11.8 - 11.9V
Across Resistor R1 4.4 - 4.1

with 0V going into R1:
Between
C & E = 12V
B & E =0V
Across Relay = 0V
Across Resistor R1 0V

Can you measure voltages and let me know what they are so can help you fault find.

You should check the transistor and diode is connected right way around.
For example if diode is connected wrong way round then excessive current will flow though transistor as rely coil will be in effected shorted, damaging transistor and diode.

Martin
Martin

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### Re: Need to make a schematic circuit

i didn't make the masurements but here is the BC337 DATASHEET see if it helps
Attachments
bc337_3.pdf

medelec35
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### Re: Need to make a schematic circuit

Data sheet is not for helping me, its for helping you.
You will need to make sure transistor (and diode) is connecting correctly.
I.e with transistor:
Emitter going to GND
Collector going to Relay and anode of diode.
Base going to 2k2 resistor

With Diode:
Cathode going to +12V
anode going to relay and collector of transistor.

You will not get any further until you take voltage measurements.
For example 5V might not even be present at pin 3 of 9way D connector/2k2 resistor so you could be looking in wrong direction and may not have an issue with transistor at all!
How will you know unless you took voltage measurements at the resistor?
Gong by it must be there because LED1 is lit won't be good enough.
What if connection from LED1 to 2k2 resistor is open circuit.
E.g from a dry joint or tracking issue.
You could have a B to E short via PCB.
It could be a whole manor of thing causing Relay board not to work.

The only way replacing resistor will help is if you did not connect a 2k2 resistor but a completely different value.
Martin