Picaxe Trigger Unit - Activated by either short/signal input on the same connection

[superworm]

Hi Guys,

The idea is really very simple, just a circuit that triggers a 5v output from the Picaxe for a couple of seconds when it is triggered by either a short or an external input signal on the same connector.

Obviously it's very simple if I was using 2 seperate input connectors, one for a short, and one for a signal input, but to save space it would be great if I could get one connector to monitor for both.

Any ideas on how I may be able to do this?

Many Thanks

Matt

 

[Andrew Cowan]

What is the signal? A switch? This is the same as short...

What is the short between? +V and input? 0V and input?

This should be possible easily, prehaps with a diode as a mixer.

A

 

[superworm]

yes essentially the short is a switch, and the external signal would just be about 5 to 30VDC.

The short can be arranged in any way that can be sensed by the Picaxe that still allows for monitoring for the possible 5 to 30VDC signal as well.

I don't really want to have a selector switch for to select short or signal input, so it would be good if I could monitor for both at the same time with just one connection.

How would the diode be used as a mixer?

Many Thanks!

 

[westaust55]

for an external signal that can very from 5V to 30V think you will need to use a transistor as an interface is a simple divider to provide 5V when at 30V is not going to work when it is only 5V (if that is still a high level).

A better description of how you wish to connect the "short" and signal and PICAEAXE output would be a good idea.
Seems to read like you may want to do this through a single terminal/wire. Which may be possible with diodes. But first a better description or a schematic diagram

 

[Andrew Cowan]

It's possible using the PICAXE's ADC pin. See attached picture.

The value of the ADC will depend on the connection. The ADC pin will only be 5V when the short switch is shorted, and when nothing is connected it will be 0V.

A

 

[superworm]

Great diagrams Andrew! Yep that's basically the idea, however that circuit would require 2 seperate input connections, one for the short switch and one for the signal in.

Really want to get it to be just one connection, probably BNC type.

Any ideas?

Thanks once again for all your help

 

[jglenn]

You might try 2 comparators, like the LM311. Put a 100K pullup resistor on
your input. One comp has a ref of 1/2V, the other 4V. If the input is a short, it will be less than 1/2V, and the first comp will switch. If the input is greater than 4V, the second comp will switch. Comparators can have the outputs hard wired together, with a single pullup resistor, so it will act like an OR gate, either input condition will trigger the single output. Put some hysteresis in there. Positive feedback that gives a snap action, like a schmitt trigger.

 

[westaust55]

Superworm,

when you say: "the external signal would just be about 5 to 30VDC."
is that its full range and it never goes to 0 volts?

If so then have the short switch pulling the line to 0V.

SOme better idea/description from you can help !

 

[Ralpht]

Jglen's answer in post 7 is the way to go. Simple and effictive. The way I'd do it. Just get the resistors right in setting up the comparators to trigger at 1/2.