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LM2907-8n to LM2917-14n for tachometer

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fever16

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lm2917

hello sir,
i have been working on the LED tachometer for my motorcycle which uses F-V converter.in that serach i found a german site. **broken link removed**
the ckt ( http://www.fda-technology.de/images/pic_Schaltplan 1_5.gif ) in that site uses LM2907-8pin version for F-V conversion.where as i already have LM2917-14 pin in my hand.i don't want to waste those chips.so can u help me in modifying the ckt.
this is my ckt.i want to drive just 10 LED's.all i need is replacing the LM2907 with LM2917
help pls
**broken link removed**
 

lm2917 tachometer

Hi fever16

Refer to National data sheet on the LM2907-LM2917
**broken link removed**

Using the LM2917-14 in place of the LM2907-8
Code: 
2907(8) pin no.      2917(14) pin no.
   1                  1
   2                  2
   3               3 & 4
   4                  5
   5                  8
   6                  9
   7                 10
   8              11 & 12
What the LM2575 regulator output voltage? If it is more than 7.5v you will need a resistor in series with pin9 of the LM2917(14) to use the internal zener - a value of 470Ω should work ok - check data sheet for required value.

hope this helps ... Polymath
 

lm2907-8n

thanks a lot polymath.
that LM2575 regulator output voltage is 5volts only i think.as it is mantioned as LM 2575 T5,0(fixed at 5.0).thats why i used 7805(easy to get and cheap)
i modified the ckt as u said pls have a look
**broken link removed**
 

lm2907 tachometer

Hi fever16

Your circuit looks ok.

You might consider including the reverse protection diode D44 as in the original.

Placing a suitable Varistor (20~30v) from D44/7805 node to Gnd would kill any spikes that may occur on the supply and damage the 7805.

regards ... Polymath
 

lm2917 circuit

thanks i'll place one.
regarding the ckt,is it ok to place R7,R8,R9 1K resistors.
and what is the function of P1 and P2
 

lm2907

Hi fever16

Please make some effort yourself!
READ the data sheet on the LM3914. Your answers are in it!
**broken link removed**

The voltage at Pin6 is High end of comparator reference - it sets the Input Level to No.of LEDs lit.

The current out of Pin7 sets LED current - (brightness).

regards ... Polymath
 

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