Need help to trigger off 1pps

[elalto]

Hi All,

This is my first post, I like this forum so, I will not be a stranger. I would like some help with a project that is a little out of my comfort zone. I have a 1pps signal from a GPS that I need to use to close a switch. The signal I will get is @ 1Hz with a 5 volt amplitude into 50Ω. The signal is, or should be, TTL level so I need to know how to use this to "push" or simulate a N-O, momentary switch. Whatever I use needs to have a 50Ω input and a "dry" closure on ouput.

Any help or ideas will be most appreciated.

Thanks

Marcos "elalto"

 

[MikeMl]

Can the circuit in which the button is to be "pushed" share a common ground with the GPS receiver? If yes, there is one set of solutions involving a transistor or two. If no, a relay or opto-isolator may be necessary.

 

[elalto]

Hi Mike,

Thanks for your response. The trigger circuit and the "button" ciruit can't share grounds, the interface will be LMR195 coax with an SMA connector. The circuit that I need to connect to has two pads for a micro switch. A relay will be too slow, a real short, momentary closure is what I need I thought about this unit, but am at a loss as to how to connect it up.

http://www.fairchildsemi.com/ds/NC/NC7SZ384.pdf

 

[MikeMl]

I do not see that the 2FNC7SZ384 provides any isolation. It has to be powered, and the common-mode range of the voltages at A & B must be within the range of gnd to Vcc.

I would go with an opto-isolator. Drive the photo emitter (LED) with the 1Hz pulse, and use the photo transistor to short across the button. You will have to determine which end of the button is more positive than the other, and connect the photo transistor collector to the more positive end. Don't forget to limit the LED current with a suitable resistor.

 

[elalto]

Mike, you are correct, duh! I meant to indicate this device: **broken link removed** which is a CMOS bilateral switch.

OK, the opto might work although I’m concerned about the width of my 1pps signal which is very short, would the LED light enough? Long enough?

The bilateral switch seems to be able to do what I need, however, what I need to know or have input on is how to interface the 1pps to the switch or the opto. The 1pps signal comes from a $40K test device from Agilent and I would hate to damage the sync output with my circuit. Is there anything I should look for or avoid?

By the way, thanks a lot for your attention and help on this.

Marcos (elalto)

 

[MikeMl]

How narrow is the pulse?

The 74v2t66 does not provide any isolation between the GPS ground and the push-button's circuit ground. I though that is a requirement? If you are willing to give up on this, there are many ways to do it.