need help to manipulate a stress meter circuit

[fatimauzma]

hey
i working on a stress meter right now.i saw the circuit on electronics for you.
but my lecturer wants me to use two I.C instead of one and 10 leds instead of 5 as done in the circuit.
iam thinking of using a resistor between them.can any one pls help me redesign the given circuit

 

[ericgibbs]

hey
i working on a stress meter right now.i saw the circuit on electronics for you.
but my lecturer wants me to use two I.C instead of one and 10 leds instead of 5 as done in the circuit.
iam thinking of using a resistor between them.can any one pls help me redesign the given circuit

hi,
A LM3915 can already drive 10 LED's, why would you want to use two LM3915's?

 

[fatimauzma]

thanks for the suggestion.
i know dat but it seems she wants some innovation.can u plz help

 

[ericgibbs]

thanks for the suggestion.
i know dat but it seems she wants some innovation.can u plz help

hi,
You may know that the LM3915 has a 3dB logarithmic interval.?
I would have thought anyone with stress levels over 5 log intervals has a serious problem!

Look at the application notes in this datasheet for connecting two LM3915's in series.

I honestly cannot see any point in connecting two LM3915's series and using only 10 LED's.???

 

[audioguru]

Two ICs and 10 LEDs?
Simply replace the transistor with an opamp amplifier and let the LM3915 drive 10 LEDs.

The 30dB range is good because the skin resistance of people varies a lot.
Some people are very high resistance dried out old prunes and other people sweat like a pig.

 

[alec_t]

D1 seems redundant. Any suggestions on its intended purpose?

 

[audioguru]

D1 seems redundant. Any suggestions on its intended purpose?

I think D1 prevents a negative static electricity charge from destroying the transistor.

In winter in most countries the temperature is cold then the humidity of the cold air is low. When the air is heated then its humidity becomes much less. Dry air does not conduct electricity like humid air so static electricity accumulates. If you walk across a carpet then your shoes are picking up many negative electrons. When you touch the touch pads you are applying thousands of negative volts but then the diode conducts when the negative input is -0.7V.

 

[alec_t]

Yup, that makes sense. It won't do much for a positive charge though ;-)

I agree with your suggestion. A lot of lecturers/tutors these days seem incapable of setting projects unambiguously; perhaps because they're only one step ahead of their students in the subjects they profess to teach.