Hi all,

I had a recent technical assesment at an interveiw, all went well apart from a few questions such as this one - please see diagram above (which may have a few slight errors - sorry!).

Firstly, I have never seen the "cog" symbol in electronics before, I guess that just means a varying voltage range between 0 and 40V (as per the label)?!

Also, there was a signal drawn with the diagram (top left) but this wasn't explained either...

Does anyone recognise this circuit? Do you know what it does?

One of the questions was "what is the Voltage at Va and Vb"... any thoughts?

Not too sure if this is really easy and I was overcomplicating things?!

Thanks all in advance

 

It makes little sense to me.

You put connection dots at Va and Vb which would imply no connections at the wire crossings. If there are connections, the inputs are shorted. How are inputs being driven? The cog symbol is meaningless to me.

What input parameters were given? The input range might go to ground, but unlikely to go to 35V above V+.

 

The cog makes me think it might be an amplifier for an inductive pickup or other kind of rpm sensor. The circuit is unfamiliar to me.

What position were you interviewing for?

 

The cog might be the knob on a power supply. Just means 'adjustable'. Beyond that, the circuit makes no sense.

 

Unfortunately your circuit looks like it could be an erroneous copy of a number of different configurations, depending upon the error. With the re-arrangement of a few parts it could be a differential amplifier to reduce the voltage range from the transducer or whatever it is to within the common mode range of the opamp.


Just a guess.

Differential amplifier <= Link to Wikipedia article

 

Here's http://datasheets.maximintegrated.com/en/ds/MAX9924-MAX9927.pdf a datasheet with a COG.

 

Here's http://datasheets.maximintegrated.com/en/ds/MAX9924-MAX9927.pdf a datasheet with a COG.

Exactly what I expected.

 

It makes little sense to me.

You put connection dots at Va and Vb which would imply no connections at the wire crossings. If there are connections, the inputs are shorted. How are inputs being driven? The cog symbol is meaningless to me.

What input parameters were given? The input range might go to ground, but unlikely to go to 35V above V+.

Thanks for that... yes, nothing was really explained i.e. input parameters... all that there was was the cog symbol with a voltage range, and a signal (top left) with no other explaination...

The cog makes me think it might be an amplifier for an inductive pickup or other kind of rpm sensor. The circuit is unfamiliar to me.

What position were you interviewing for?

Thanks for that... the role was for an "Electronic Engineer"...

Unfortunately your circuit looks like it could be an erroneous copy of a number of different configurations, depending upon the error. With the re-arrangement of a few parts it could be a differential amplifier to reduce the voltage range from the transducer or whatever it is to within the common mode range of the opamp.

View attachment 137409
Just a guess.

Differential amplifier <= Link to Wikipedia article

Thanks for that... yes, before the interview I brushed up on op-amps etc and memorised all the common circuits (non-inv, inv, differentiial, integrator etc) but when I saw this it totally threw me... didn't recognise the cog, the signal in the top left wasn't explained etc. I have since googled it and looked through old text books but couldn't find anything similar! Thanks again

Here's http://datasheets.maximintegrated.com/en/ds/MAX9924-MAX9927.pdf a datasheet with a COG.

Ah ok, brilliant.. so the cog represents some type of rotating device (crankshaft, transmission shaft etc)... so I guess the circuit would be to measure rotation speed and give an output dependant on that...