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3mm bulb connection

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3mm bulb connection
Posted by hwolf on Wednesday, May 03, 2017 2:31 PM
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Posted by maxman on Wednesday, May 03, 2017 3:20 PM

So those are LEDs, or are they bulbs?

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Posted by gregc on Wednesday, May 03, 2017 3:29 PM

A single-pole/single-throw (SPST) switch has 2 connections.   Your drawing suggests a single-pole/double-throw (SPDT) switch which makes a connections between a common terminal and one of the other two.

the two bulbs, a single resistor and SPDT switch suggests that you want to the switch to turn on one or of the two lamps.

why is there a resistor?  An incandecent bulb is normally connected to power at the voltage the bulb is rated at.   Do you mean LED instead of bulb?  Connect the anode end of an LED to the switch.

 

   V+ --o  --o --- bulb ------ resistor ---- Gnd
\--o --- bulb --|

connect the common terminal of the switch to power.
connect each of the other two switch terminals to one lead of each bulb
connect the other lead of each bulb together and to the resistor.
connect the other resistor lead to ground

the switch provides power on bulb or the other

greg - Philadelphia & Reading / Reading

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Posted by hwolf on Wednesday, May 03, 2017 4:22 PM

These are LED's.

The switch turn one light on if you throw to the left and turns on the other light if you throw to the right.

 left

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Posted by rrinker on Wednesday, May 03, 2017 4:29 PM

 Short lead of one LED to the left pin of the switch. Short lead of other LED to the right pin of the switch. Resistor to the middle pin. Other side of resistor to power supply -, the two free longer leads of the LEDs to the poswer supply +.

Just flip the LED on the right in your picture and the leads line up exactly where they need to connect.

                                   --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by hwolf on Wednesday, May 03, 2017 7:03 PM

Randy

I forgot.  12vdc  or 18vac

Harold

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Posted by rrinker on Wednesday, May 03, 2017 7:20 PM

12V DC. What value resistor do you have? 1K is probably good.

                   --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by richg1998 on Wednesday, May 03, 2017 8:21 PM

hwolf

Randy

I forgot.  12vdc  or 18vac

Harold

 

As Randy said, 1k is good for 12 vdc and allows about 10 ma of currecnt.

If you used 18 vac, 1.8 k would allow about the same current.

Some suggest a protective diode when using AC.

Ohm's law calculator.

https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-ohms?&WT.srch=1&gclid=CL_B876J1dMCFdQ9gQodUkgOsw

Rich

N

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Posted by hwolf on Thursday, May 04, 2017 6:18 AM

Thanks Randy

It is a 1K.

Harold

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Posted by hwolf on Thursday, May 04, 2017 12:41 PM

Ok Now we have another problem.

All wiring is per your post and all solder joint are tight.  When I throw the switch to the left the green light goes on as it is supposed to. When I throw the switch to the right the red Led does not light. 

What reading should I get on my meter set to DC and using the drawing above where should I place the leads from the meter

The power supply lead on one side of the resistor is 9.89v and on the other side of the resistor is 1.84v

Harold

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Posted by gregc on Thursday, May 04, 2017 5:41 PM

rrinker
 Short lead of one LED to the left pin of the switch. Short lead of other LED to the right pin of the switch. Resistor to the middle pin.

are you sure the middle pin is the common?

greg - Philadelphia & Reading / Reading

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Posted by gregc on Friday, May 05, 2017 5:57 PM

I believe Randy described wiring the circuit as below 

 

     |--- LED ---o (A)
| \
V+ --| o--- resistor ---- Gnd
| .
|--- LED ---o (B)


check the voltage between the LED/Switch (A/B) connections and ground. When the LED is on, there should be a small voltage and a higher voltage when the LED is off. If the LED is off and there is no voltage, the LED may be backwards.

it's also possible the switch is miswired, an LED is connected to the common terminal instead of the resistor (shown below).
|--- LED ---o (A)
| | .
V+ --| | o--- resistor ---- Gnd
| |
|--- LED ---o (B)

With the circuit unpowered, measure the resistance between the terminal connected to the resistor and the other two terminals.   Depending on the switch position, one or the other should be low resistance.

greg - Philadelphia & Reading / Reading

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Posted by BigDaddy on Friday, May 05, 2017 6:24 PM

rrinker
Just flip the LED on the right in your picture and the leads line up exactly where they need to connect.

Did you remember to that?

Henry

COB Potomac & Northern

By the Chesapeake Bay

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Posted by rrinker on Saturday, May 06, 2017 10:26 AM

 Be one of the first SPDT toggles I've seen where the middle wasn't the common. I suspect polarity is just reversed on the red LED.

                            --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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