16mm Illuminated Latching Pushbutton Switch

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MrHeisenberg
 
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16mm Illuminated Latching Pushbutton Switch

Post by MrHeisenberg »

This is my first post. I am a retired mechanical engineer . . . I am NOT an electrical engineer. I have a project where I wish to use all 5 colors of the subject switch: 1442 (Red), 1443 (Green), 1444 (Yellow), 1476 (Blue), and 1478 (White). I have 2 lines of questions:
1. I have no intention of powering a load. The switches will be installed on a new grandchild's 'busy board' and will have (8) AA batteries in series as the power source (12V, 2000mAh), with the 5 switches connected in parallel. I simply want the LED to light when the button is pushed once, and turn off when the button is pushed a second time. Does anyone have a wiring diagram to show how to accomplish this? The product pages all indicate "The LED is separated from the button, so you can make it light up when on, light up when off, always lit, etc." My current thinking is to sequence the wiring in this fashion (see attachment): + terminal of power source to + terminal on switch, + terminal on switch to + terminal on LED, - terminal on LED to resistor to - terminal on switch, - terminal on switch to - terminal on power source. Does this make any sense? Further, am I correct that the LED terminals are the thicker terminals below those labeled + and -?
2. Regarding resistor sizing: The 1442, 1443 and 1442 switches all indicate a forward voltage of 2.2V, however, the 1476 and 1478 indicate a forward voltage of 3V. Are the specifications between the two groups of switches really different? Further, is 20mA a good number to use for the forward current? If so, to be technically accurate, I would come with 510ohms for the 1442, 1443 and 1442, and 470ohms for the 1476 and 1478. Does this appear to be sound thinking?
Thank you for your time.
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Pushbutton Back.jpg
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dastels
 
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Re: 16mm Illuminated Latching Pushbutton Switch

Post by dastels »

The terminals (thin ones) labelled /- are the LED. The thicker, unlabelled terminals are the switch. the switch has no +/- .

As for your wiring...no. That would put the switch directly across the power source. The batteries would probably catch fire and/or explode. Also, you have the LED in parallel with the switch. Try:
- power + to one side of the switch
- other side of the switch to one side of the resistor
- other side of the resistor to LED +
- LED - to power -

Closing the switch completes the circuit, allowing current to flow through the resistor and LED.
The difference is LED forward voltages is due to differences in the properties of the LEDs that result in different colors.
For the resistors you want values that will account for voltage in excess of the forward voltage of the LED, at nominally 20mA. R = V/I so
(12v - 2,2v)/0.02A = 490 ohms
(12v - 3v)/0.02A = 450 ohms

One question I have is why are you using 12v? You need at least 3v for the LEDs, anything in excess of that is wasted in the resistor. If you don't have a strong reason to use 8 calls, 3 or 4 (nominally 4.5 or 6v) would do. Cell voltage is dependant on battery type so using more than a nominal 3v is a good idea, but too much more is a waste. Whatever you end up using, use the above equations replacing 12v with what you use. Exact resistor values aren't too important, get the closest you can find. Typical resistors are +/- 5% or 10%. You can get 1% resistors if you're willing to pay the premium, but for this it's nowhere near worth it.

Dave

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MrHeisenberg
 
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Re: 16mm Illuminated Latching Pushbutton Switch

Post by MrHeisenberg »

Hi, Dave. Thank you for being patient with a mechanical guy.

1. I sketched up what I think you were describing in words (see attachment). Can you validate this is correct?
2. Thank you for asking the question about 12V. I have other elements in the circuit: 12V buzzer, 12V flashing light, and 12V fixed light, all run by other switches. However, you caused me to re-think things. I have written questions to each manufacturer to see if 6V would adequately drive those elements. If so, I will drop back to 6V . . . great catch and question!
3. Thanks for validating my resistor sizes (based on 12V). I had come up with the same numbers and went with the closest size up resistor for each . . . 510 ohms and 470 ohms respectively. I will re-size if I go with 6V.
4. NEW QUESTION: Do you (or anyone) happen to know what size spades are on the back of the switch?

Again, thank you for your time.
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LED Switch Circuit.jpg
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dastels
 
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Re: 16mm Illuminated Latching Pushbutton Switch

Post by dastels »

The diagram looks good.

I don't know the sizes of the spade terminals, and I don't have any of those particular switches on hand. I'll see what I can find out.

Dave

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