Push button switch & LED

[StanO]

I know I have seen others posts identifying push button switches and LED hook ups. My searching TRF has not been successful.

On the internet I find only a few push button switches with embedded lights, but they tend to be 120V AC or 12V DC. I assume the light will not work with lower voltages.

Can I assume a switch that has a higher voltage than say 9V will work as long it can carry enough Amps for the ematch? Then assuming I want to hook up an LED I can use calculators like;

https://www.quickar.com/noqbestledcalc.htm https://led.linear1.org/1led.wiz

to calculate the resistance needed?

What do the TRF folks recommend for push button switches and attendant LED?

Thanks,
StanO

 

[Steve Shannon]

First, yes, as long as a switch is rated to handle enough current (amperes) and at the proper DC voltage or higher, you could use it. Those two ratings are independent of each other though. Don't multiply them to get a power rating and then look for something equivalent.
What do you want the LED to do? I can help you learn how to add a current limiting resistor.

 

[KenRico]

If you use a 5M LED String it already has upto 300LED and resistors..just add Power ...even a small 3S can light up the night

If you go RGB instead of 1 color you will need a Mini Controller. With the 1 color if you want it to blink they have a mini dimmer .

Kenny

 

[StanO]

Steve, In ignorance I bought 2 types of push button switches. The purpose was to arm EasyMini altimeters instead of using screw switches. The EasyMini has connections for the power switch. I plan to use 9v batteries initially and Lipos later. I do not plan to use a separate pyro battery. Basically, even though the altimeter will beep continuity, I would like to have an easier way to arm it and know the circuit is live.


One switch, the Radio Shack 275-0009, is a 3A 125V illuminated push button switch. It has two connections for the power and 2 connections indicating 1.7V DC. The power draw for the light isn’t specified. What’s next?


The second switch is not illuminated but rated at 3A 125V. With that one I assume I would have to add an LED and resistor to the circuit. What do you recommend for the LED, where can I get one and appropriate resistor?


Thanks for your help
StanO

First, yes, as long as a switch is rated to handle enough current (amperes) and at the proper DC voltage or higher, you could use it. Those two ratings are independent of each other though. Don't multiply them to get a power rating and then look for something equivalent.
What do you want the LED to do? I can help you learn how to add a current limiting resistor.

 

[Steve Shannon]

First, I'm prejudiced against Radio Shack quality switches in general. Second, I'm prejudiced against push button switches specifically. The contacts in push button switches are held in contact by springs that allow them to bounce out of contact. However, it's your choice to make and I'll get off my soapbox. I've seen a lot of successful flights using RS push button switches and only one failure.
With that confession out of the way, what's the purpose of the LED? Do you want it illuminated when you power the avionics (switch on)? That's going to slightly shorten the life of the battery. The LED and a resistor must be in parallel with the altimeter. Then, when the switch is on power goes to both the altimeter and the LED and resistor, which are in series.
Does the blister card for the first switch have a schematic of any kind?
An LED causes a voltage drop, somewhere between 0.5 and 1 volt. It's part of the spec for the LED. I buy mine from Digikey, or Allied, but you probably just ought to pick up some marked extra bright from Radio Shack that have a form factor you want.
If you're using the LED with a 9 volt battery, subtract the voltage drop from the actual highest voltage of the battery. Let's say your new battery puts out 9.7 volts. Let's also assume the forward voltage drop for the LED is 0.7 volts. The remainder is 9 volts.
Another spec for the LED is the current, marked i in the spec. It may be around 20 mA. You'll want to get it from the package or data sheet. Assuming 20 mA, or 0.020 A, and using v = i*R, we solve for R to get the value of the resistor. R = v/i, so R = 9.0/0.020, or 450 ohms. That's not a standard resistor size, so pick one closest to it, which is probably 470 ohms. Recalculate the actual current using 470 ohms and you get 0.019 A.
Power dissipated by the resistor is i^2 * R, or 0.019 * 0.019 * 470 = 0.172 watt, so a quarter watt resistor is fine.
So, if that makes sense to you, pick out some LEDs from Radio Shack's website or local store and then we'll work through calculating what size resistor to buy, also from Radio Shack.
I hope that all makes sense.

 

[astrojase]

I've been playing with LED's and Altimeters for a little while now - my hearing 'aint what it used to be' and my Uncle is L3 and HAS hearing aids, so I'm trying to be helpful to him as well.

If you put the LED/resistor in series with the battery/switch it will draw current away from the altimeter, which may not be ideal - it might be perfectly fine, obviously depends. It will always be on, so constantly draw current...

A couple of altimeters that I use regularly are the Missile Works RRC3 and Perfectflite Stratologger, and just got a couple of Perfectflite CF's with the LED output on the board. With the CF's you'll need a JST 3 pin connectors (or buy one from them with LED complete). With the RRC3 you can set the AUX output to Sync with LED - which is perfect! Hell, I use a red LED for the Perectflite CF and blue LED for the RRC3 - matches the corresponding PCB colors... The CF output voltage is 3.3V (documented) and the RRC3 output voltage from the AUX is ~7.8V (measured with my cheap multimeter so YMMV)... as Steve points out above simple ohms law or an online LED calc https://led.linear1.org/1led.wiz is all you need thereafter to calculate what type of resistor you'll need.

The LEDs are only on momentarily/whilst 'blinking' out what the altimeter is doing - so obviously don't draw down the batteries as much as if you had them constantly on...you really don't need a power indicator LED, if your LED are blinking you know they are on!!!

Actually, (Just remembered) I uploaded a clip about this a while back:
[video]https://youtu.be/cIEFTfYnhCw[/video]

 

[Steve Shannon]

I've been playing with LED's and Altimeters for a little while now - my hearing 'aint what it used to be' and my Uncle is L3 and HAS hearing aids, so I'm trying to be helpful to him as well.

If you put the LED/resistor in series with the battery/switch it will draw current away from the altimeter, which may not be ideal - it might be perfectly fine, obviously depends. It will always be on, so constantly draw current...

A couple of altimeters that I use regularly are the Missile Works RRC3 and Perfectflite Stratologger, and just got a couple of Perfectflite CF's with the LED output on the board. With the CF's you'll need a JST 3 pin connectors (or buy one from them with LED complete). With the RRC3 you can set the AUX output to Sync with LED - which is perfect! Hell, I use a red LED for the Perectflite CF and blue LED for the RRC3 - matches the corresponding PCB colors... The CF output voltage is 3.3V (documented) and the RRC3 output voltage from the AUX is ~7.8V (measured with my cheap multimeter so YMMV)... as Steve points out above simple ohms law or an online LED calc https://led.linear1.org/1led.wiz is all you need thereafter to calculate what type of resistor you'll need.

The LEDs are only on momentarily/whilst 'blinking' out what the altimeter is doing - so obviously don't draw down the batteries as much as if you had them constantly on...you really don't need a power indicator LED, if your LED are blinking you know they are on!!!

Actually, (Just remembered) I uploaded a clip about this a while back:
[video]https://youtu.be/cIEFTfYnhCw[/video]

That truly is the better way to go, for all the reasons posted!


[emoji1010] Steve Shannon [emoji1010]

 

[StanO]

I've been playing with LED's and Altimeters for a little while now - my hearing 'aint what it used to be' and my Uncle is L3 and HAS hearing aids, so I'm trying to be helpful to him as well.

If you put the LED/resistor in series with the battery/switch it will draw current away from the altimeter, which may not be ideal - it might be perfectly fine, obviously depends. It will always be on, so constantly draw current...

A couple of altimeters that I use regularly are the Missile Works RRC3 and Perfectflite Stratologger, and just got a couple of Perfectflite CF's with the LED output on the board. With the CF's you'll need a JST 3 pin connectors (or buy one from them with LED complete). With the RRC3 you can set the AUX output to Sync with LED - which is perfect! Hell, I use a red LED for the Perectflite CF and blue LED for the RRC3 - matches the corresponding PCB colors... The CF output voltage is 3.3V (documented) and the RRC3 output voltage from the AUX is ~7.8V (measured with my cheap multimeter so YMMV)... as Steve points out above simple ohms law or an online LED calc https://led.linear1.org/1led.wiz is all you need thereafter to calculate what type of resistor you'll need.

The LEDs are only on momentarily/whilst 'blinking' out what the altimeter is doing - so obviously don't draw down the batteries as much as if you had them constantly on...you really don't need a power indicator LED, if your LED are blinking you know they are on!!!

Actually, (Just remembered) I uploaded a clip about this a while back:
[video]https://youtu.be/cIEFTfYnhCw[/video]

Thanks for suggestions & comments. Much appreciated! After looking at the RRC3 & Stratologger online I am going to get the RRC3. As hearing loss is one of my issues I liked that you can set the AUX output to Sync with LED. The RRC3 will have a simple switch. I plan to use redundant deploy so will also hook up switch & LED for my EasyMini. I want the knowledge & experience.

Thanks,
StanO

 

[astrojase]

Sounds like a great plan, Stan

Just quickly, and check with the good folks at Altus before you try this, with the old Stratologger (SL100) I put an LED in parallel with the piezo speaker :wink:, as it is outputting the signal you want... Now that is just an idea, and again, you'd definitely want to check with the EasyMini folks before you try it - they would most probably have a better suggestion for you.

 

[cavecentral]

All I know is I used a switch w/ LED from radioshack in 2011 for my first altimeter. Attempted L2 flight with it and the perfect flight would tell me that battery was dead. I swapped batteries, then altimeters, no joy. Did L2 with motor ejection. Later realized the LED drain was the issue and the drain made it fail the min-voltage test on startup.

Never revisited this. Just something to watch out for. I do think I had it arming properly, but might have had the USB powering it as well using the software to test the various circuits and set the main altitude.

 

[astrojase]

All I know is I used a switch w/ LED from radioshack in 2011 for my first altimeter. Attempted L2 flight with it and the perfect flight would tell me that battery was dead. I swapped batteries, then altimeters, no joy. Did L2 with motor ejection. Later realized the LED drain was the issue and the drain made it fail the min-voltage test on startup.

Never revisited this. Just something to watch out for. I do think I had it arming properly, but might have had the USB powering it as well using the software to test the various circuits and set the main altitude.

I think putting the LED on the switch circuit is probably not the way to go - the SL100 also has a 3 pin JST audio output @ 3.3V so you could hook the LED up to that without any problems.

I suggested to place the LED in parallel to the piezo as an idea for the EasyMini (but again please check with the mfg first) as an alternative 'output' source.

 

[StanO]

First, I'm prejudiced against Radio Shack quality switches in general........
I hope that all makes sense.

Steve, thanks for your feedback and “prejudices.” Much appreciated! I will be going with an RRC3 as one of my altimeters that has an LED on it. I will use a screw switch. See post to astrojase. And yes it makes sense.

Sorry, I had a reply earlier and lost it. Had to query RS for info then determined what would and wouldn’t work from my first purchase. But I have been to Radio Shack since and picked up some parts per your suggestion. I still want to hook up an LED/push button switch for the backup altimeter. I may change to a different kind of switch later.

I purchased an LED Based on the specs below and 2 different resistors. One resistor is 470 Ohm at 1/8 watt and the other is 270 Ohm at ½ watt. Radio Shack had a very limited selection. Using your formulas and a battery voltage of 9.5V, I calculate a needed resistance of 390 Ohm and .156 watt.

LED:
Forward Voltage 1.7 typ; 2.4 max
Amp 20mA

So is the 470 Ohm resistor too much?

Thanks,
StanO

 

[StanO]

I think putting the LED on the switch circuit is probably not the way to go - the SL100 also has a 3 pin JST audio output @ 3.3V so you could hook the LED up to that without any problems.

I suggested to place the LED in parallel to the piezo as an idea for the EasyMini (but again please check with the mfg first) as an alternative 'output' source.

astrojase, thanks for the suggestion. Will talk to mfg if I do that

 

[astrojase]

No worries

Regarding your resistor question above, simply put, the 470 ohm resistor will be fine.

 

[Steve Shannon]

Steve, thanks for your feedback and “prejudices.” Much appreciated! I will be going with an RRC3 as one of my altimeters that has an LED on it. I will use a screw switch. See post to astrojase. And yes it makes sense.

Sorry, I had a reply earlier and lost it. Had to query RS for info then determined what would and wouldn’t work from my first purchase. But I have been to Radio Shack since and picked up some parts per your suggestion. I still want to hook up an LED/push button switch for the backup altimeter. I may change to a different kind of switch later.

I purchased an LED Based on the specs below and 2 different resistors. One resistor is 470 Ohm at 1/8 watt and the other is 270 Ohm at ½ watt. Radio Shack had a very limited selection. Using your formulas and a battery voltage of 9.5V, I calculate a needed resistance of 390 Ohm and .156 watt.

LED:
Forward Voltage 1.7 typ; 2.4 max
Amp 20mA

So is the 470 Ohm resistor too much?

Thanks,
StanO

Using the typical fwd voltage and your battery: 9.5v - 1.7v = 7.8v
Then using Ohm's law again: v = i * r,
7.8v = i * 470, rearrange using algebra,
i = 7.8/470 = 0.0165, just under 17 ma.

Power is 7.8 x 0.0165 = 0.129. That's very slightly over 1/8 watt, but not enough to matter.
That should be just fine as others have already said, but now you know how much.

If that's too dim you can always go to the next smaller resistor or put multiple resistors in series to get exactly what you want. If you do, current will rise, driving power up exponentially. The resistor could get warm. [emoji33]

 

[StanO]

Using the typical fwd voltage and your battery: 9.5v - 1.7v = 7.8v
Then using Ohm's law again: v = i * r,
7.8v = i * 470, rearrange using algebra,
i = 7.8/470 = 0.0165, just under 17 ma.

Power is 7.8 x 0.0165 = 0.129. That's very slightly over 1/8 watt, but not enough to matter.
That should be just fine as others have already said, but now you know how much.

If that's too dim you can always go to the next smaller resistor or put multiple resistors in series to get exactly what you want. If you do, current will rise, driving power up exponentially. The resistor could get warm. [emoji33]

I see I missed a step. Now have calcs straight. Thanks!