Voltage on a Apex Breakout Box?

[mike550]

I’m thinking about using LED-lit switches on a breakout box. The goal would be that when the circuit is closed that an LED would illuminate. Does anyone know what the voltage is across the terminals?

Thanks in advance.

 

[Biglew11]

Any where from 2.5v to 5v, and not enough current to drive anything just enough to sense weather a switch is open or closed.

 

[mike550]

Any where from 2.5v to 5v, and not enough current to drive anything just enough to sense weather a switch is open or closed.

Thanks @Biglew11 That would explain why no one is using illuminated switches or status LEDs. I suppose I could just pit a DC voltmeter across it and see what the voltage is. If I decide to hack something with status lights on a BoB I’ll make sure to post.

 

[Biglew11]

Thanks @Biglew11 That would explain why no one is using illuminated switches or status LEDs. I suppose I could just pit a DC voltmeter across it and see what the voltage is. If I decide to hack something with status lights on a BoB I’ll make sure to post.

it may be doable with a digital type sensing circuit. but it would probably cause interference with the breakout box being able to sense an open or closed switch.

 

[theatrus]

Thanks @Biglew11 That would explain why no one is using illuminated switches or status LEDs. I suppose I could just pit a DC voltmeter across it and see what the voltage is. If I decide to hack something with status lights on a BoB I’ll make sure to post.

It uses pull-ups and series limiting resistors, which doesn't allow for powering directly from the port. Putting any load on it should drop the voltage pretty quickly - don't just measure open circuit voltage.

 

[mike550]

It uses pull-ups and series limiting resistors, which doesn't allow for powering directly from the port. Putting any load on it should drop the voltage pretty quickly - don't just measure open circuit voltage.

Thanks @theatrus -- my thought was that once I know the open circuit voltage that I could put an appropriately sized LED in series with a switch. Of course I would simply put the LED across the port to see what happens -- and hopefully not let out any of the magic blue smoke.

 

[NinjaTiLL]

Thanks @theatrus -- my thought was that once I know the open circuit voltage that I could put an appropriately sized LED in series with a switch. Of course I would simply put the LED across the port to see what happens -- and hopefully not let out any of the magic blue smoke.

This will not work. This is a sensing circuit only. The controller most likely has pull-up resistors on each pin that only allow micro-amps to pass through the resistor to pull the pin high. When you connect a switch to the break out box, the switch connects the pin to ground. The controller senses the low state and acts upon it.

I tinker with microcontrollers all the time. I do not know the specifics of what is inside the Apex. But, most uCs use about a 47kOhm pull-up resistor. If we assume it is 5V (TTL) logic, then the pull-up resistor passes 106uA. That is not enough to power an LED indicator and would mess with the I/O pin state anyways (since most LEDs have a 2V or more forward voltage.) Most newer uCs use 3.3V logic and, if that is used here, the same 47kOhm resistor only passes 70uA. Most LEDs require about 20mA. I've seen LEDs that use single digit mA but those are rare, and dim. I've never seen an LED that pulls less than 1mA.

Good luck, let us know what you find.

 

[mike550]

This will not work. This is a sensing circuit only. The controller most likely has pull-up resistors on each pin that only allow micro-amps to pass through the resistor to pull the pin high. When you connect a switch to the break out box, the switch connects the pin to ground. The controller senses the low state and acts upon it.

I tinker with microcontrollers all the time. I do not know the specifics of what is inside the Apex. But, most uCs use about a 47kOhm pull-up resistor. If we assume it is 5V (TTL) logic, then the pull-up resistor passes 106uA. That is not enough to power an LED indicator and would mess with the I/O pin state anyways (since most LEDs have a 2V or more forward voltage.) Most newer uCs use 3.3V logic and, if that is used here, the same 47kOhm resistor only passes 70uA. Most LEDs require about 20mA. I've seen LEDs that use single digit mA but those are rare, and dim. I've never seen an LED that pulls less than 1mA.

Good luck, let us know what you find.

Thanks @NinjaTiLL -- I figured it would be very low current but never really dug into the specifics. So this is very helpful. I'm going to rethink the "cool factor" vs "effort" side of this.

 

[Biglew11]

definitely a ton of effort, you'd need to use logic circuits at the bare minimum to even have a chance of it working. almost everything you put at these pins will be seen as a closed switch, including any led.

 

[NinjaTiLL]

Thanks @NinjaTiLL -- I figured it would be very low current but never really dug into the specifics. So this is very helpful. I'm going to rethink the "cool factor" vs "effort" side of this.

There's another angle to consider. You could use a DPST (double pole single throw) switch and a separate power supply to accomplish the same thing. One side of the switch would connect to the Apex BoB and ground. The other side of the switch would connect to a separate (probably 5v) power supply, the led, a current- limiting resistor and ground. Do you need a schematic?

 

[Biglew11]

There's another angle to consider. You could use a DPST (double pole single throw) switch and a separate power supply to accomplish the same thing. One side of the switch would connect to the Apex BoB and ground. The other side of the switch would connect to a separate (probably 5v) power supply, the led, a current- limiting resistor and ground. Do you need a schematic?

this will work very well if op doesn't mind a separate indicator light.
if you have open 24v ports you can run an indicator off those and some programing to turn on off with the BoB switch.

 

[TheHarold]

I make LED switch boxes all the time, both with LED buttons and LED toggles. You CANNOT use the signal voltage of the breakout box, instead use an external power supply or the eb832 24v accesory port.

You also need to ensure you are not allowing power to enter the breakout box- the power side and signal side must be fully isolated or risk damaging your apex.

 

[minus9]

I made my own toggle box, but used led buttons that have isolated power for always on display. If you wire it to illuminate when pushing the button, then you pass the voltage, which is a no, no.

There may be latching led buttons that have isolated power?

 

[simsimsim]

Here is one that uses LED switches, the LEDs only go on when the switches are in the ON position. It does not send power to the BOB. the power is on a separate circuit.

available here

 

[TheHarold]

Here is one that uses LED switches, the LEDs only go on when the switches are in the ON position. It does not send power to the BOB. the power is on a separate circuit.

available here

What toggles are you using, that have LEDs on a separate circuit? Those aren’t the standard 3-prong LED toggles? Or are you incorporating individual relays?

 

[simsimsim]

What toggles are you using, that have LEDs on a separate circuit? Those aren’t the standard 3-prong LED toggles? Or are you incorporating individual relays?

They are the standard 3-prong LED toggles. Yes each switch has a relay.