What does this mean by isolated?

[blis]

Hi, I'm just starting out learning about electronics.

This frequency counter has 2 sets of pins. 1 for isolated input and the other for non isolated.

I'm not really sure what this means. From the googling I've been doing all I can tell is it might have something to do with grounding

I'm wanting to use it to measure the output from a simple 555 square wave generator running off a 9 volt battery. Should I connect it to the isolated or non-isolated input?

Sorry if I'm in the wrong forum. Any help is appreciated.

 

[gorgon]

As long as your signal source is from a battery supplied system, you can use both.

An isolated input is normally used where the signal source is far away or has a different power supply, and will inhibit ground loop noise to interfere with the signal. It is also preferable to use this when your system is taking input from external sources.

Normally it should be ok to use the non isolated input if your system is local, and powered from the same source, or battery as in your example.

TOK

 

[blis]

Thanks mate. Much appreciated

 

[TedA]

blis,

There is no telling what the vendor means. There is no absolutely standard technical meaning of the word, and English is not the vendor's first language.

There may be a capacitor in series with the hot side to isolate the counter circuit from DC on the input. There might be two capacitors, one for each side of the input. There could be a series resistor. There could be a transformer that would provide what gorgan is thinking about as isolation. There could be some combination of these things, or something else.

The information on the vendor's web page does not seem to tell us anything about the relative characteristics of the two inputs. See if you can get a schematic, or explanation from the vendor.

If you already have the counter unit, an ohmmeter can tell you a great deal. ( Request instructions for this, if we can help.) If in doubt, you might place a small capacitor and a resistor in series with your signal.

It is possible that the nearly 9Vpp signal straight off the 555 would be too much for the counter's input circuit. Without additional knowledge about the counter's inputs, I believe I'd start with the series RC network on either input I was using. 10k & .01 uF might be good values for a start.

Where are you located? You should try to find a nearby "Elmer" who can help you out. It would be really nice if someone with an oscilloscope could help you see what's going on with your circuits. You can do this in isolation; this forum helps make that work, but someone nearby with knowledge, test equipment and time can be a real help.

Ted

Ted

 

[blis]

Thanks for taking an interest Ted, I appreciate it.

The manual says its input voltage can be between 5 and 12 volts so I should be alright there hopefully but they dont mention anything about how the inputs differ. I'll email them and see what they say.

I'm not really sure what RC networks do but the counter wont arrive for another 2 or 3 weeks so that gives me plenty of time to read up on them.

I'm in Glasgow in Scotland btw. Havent actually built any cicuits yet though. Just studying till everything gets delivered.

 

[selanac]

Just curious Ted A., what is an Elmer?

BTW, I believe www.Electronics-DIY.com sells Frequency Counter kits among other kits.

 

[TedA]

selanac,

"Elmer" is a ham radio term for mentor. You know, the old guy across the street who tinkers with radios in his basement, and is willing to take some time to help the neophyte.

blis,

I'm sure someone around Glasgow would fit this description. Look for the nearest RSGB chapter, even if radio is not your specific interest.

And don't worry about asking dumb questions. You will have to be very ingenious indeed to out-dumb some of the questions asked on this forum!

Ted

 

[gorgon]

blis,

There is no telling what the vendor means. There is no absolutely standard technical meaning of the word, and English is not the vendor's first language.

There may be a capacitor in series with the hot side to isolate the counter circuit from DC on the input. There might be two capacitors, one for each side of the input. There could be a series resistor. There could be a transformer that would provide what gorgan is thinking about as isolation. There could be some combination of these things, or something else.

Ted

From the pictures of the PCB it looks like an optocoupler is used for the isolation purpose, but I could be wrong.

TOK