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problem with LM 2917 , LM 3914

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kreka

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I made a circuit using lm2917 and lm3914 to get LED RPM

i got 2 problem

1- after connecting the circuit with 12V power some LED's light ( it must not light as it light when freq increase then they start light one by one )

2- when i increase my car RPM LED's of 2nd ic lm3914 don't respond .

i made this circuit 2 times so i am sure i didn't made and wrong connection

can i get any help ??

**broken link removed**
 
IC3 is set to indicate an input voltage from 0V to +1.25V. Then you should set IC4 indicate an input voltage from +1.25V to +2.5V.
 
What is the voltage on pin 5 of the LM3914's?
the voltage is the output from LM 2917 increase when freq increased
IC3 is set to indicate an input voltage from 0V to +1.25V. Then you should set IC4 indicate an input voltage from +1.25V to +2.5V.


sorry i can't understand the point as i have little info about electronics

and the problem of ic4 connection cuz which problem ??
 
Sorry, you DO have IC3 and IC4 connected correctly.

But the LM2917 is wrong. The input must be ONLY a positive voltage pulse but yours is AC which swings negative half the time.
The input of an LM2917 must NEVER be negative but the input of an 8-pins LM2907 or LM2917 can go negative.
 
Sorry, you DO have IC3 and IC4 connected correctly.

But the LM2917 is wrong. The input must be ONLY a positive voltage pulse but yours is AC which swings negative half the time.
The input of an LM2917 must NEVER be negative but the input of an 8-pins LM2907 or LM2917 can go negative.

no no all freq input in LM2917 is positive never goes negative
 
I think he is talking about C1. If your pulse is always 0 to 12 volts why do you need it?

The differential input options (LM2907, LM2917) give the user
the option of setting his own input switching level and still have
the hysteresis around that level for excellent noise rejection
in any application. Of course in order to allow the inputs to
attain common-mode voltages above ground, input protection
is removed and neither input should be taken outside the limits
of the supply voltage being used. It is very important that
an input not go below ground without some resistance in its
lead to limit the current that will then flow in the epi-substrate
diode.

The 10k may be enough to protect it.
 
Last edited:
no no all freq input in LM2917 is positive never goes negative
You have input pin1 connected to 0V with R2. Then you capacitor-couple the input frequencies with C1 so that the input swings positive and negative. But it must never go negative.

The datasheet shows a 14-pins LM2917 tachometer with breaker points at the input. The breaker points do not have a coupling capacitor because they are DC-coupled and go from 0V to +12V. Pin 11 is biased at +0.7V with a resistor and diode so that the signal is detected going above and below +0.7V.

What produces your input signal?
 
One of these may have somethig to do with your first problem where some leds are on with no input.

Application Hints
Three of the most commonly needed precautions for using
the LM3914 are shown in the first typical application drawing
showing a 0V–5V bar graph meter. The most difficult problem
occurs when large LED currents are being drawn, especially
in bar graph mode. These currents flowing out of the
ground pin cause voltage drops in external wiring, and thus
errors and oscillations. Bringing the return wires from signal
sources, reference ground and bottom of the resistor string
(as illustrated) to a single point very near pin 2 is the best
solution.
Long wires from VLED to LED anode common can cause
oscillations. Depending on the severity of the problem
0.05μF to 2.2μF decoupling capacitors from LED anode
common to pin 2 will damp the circuit. If LED anode line
wiring is inaccessible, often similar decoupling from pin 1 to
pin 2 will be sufficient.
If LED turn ON seems slow (bar mode) or several LEDs light
(dot mode), oscillation or excessive noise is usually the
problem. In cases where proper wiring and bypassing fail to
stop oscillations, V+ voltage at pin 3 is usually below suggested
limits. Expanded scale meter applications may have
one or both ends of the internal voltage divider terminated at
relatively high value resistors. These high-impedance ends
should be bypassed to pin 2 with at least a 0.001μF capacitor,
or up to 0.1μF in noisy environment.
 
I think he is talking about C1. If your pulse is always 0 to 12 volts why do you need it?

The differential input options (LM2907, LM2917) give the user
the option of setting his own input switching level and still have
the hysteresis around that level for excellent noise rejection
in any application. Of course in order to allow the inputs to
attain common-mode voltages above ground, input protection
is removed and neither input should be taken outside the limits
of the supply voltage being used. It is very important that
an input not go below ground without some resistance in its
lead to limit the current that will then flow in the epi-substrate
diode.

The 10k may be enough to protect it.
no input from car battery may go high
You have input pin1 connected to 0V with R2. Then you capacitor-couple the input frequencies with C1 so that the input swings positive and negative. But it must never go negative.

The datasheet shows a 14-pins LM2917 tachometer with breaker points at the input. The breaker points do not have a coupling capacitor because they are DC-coupled and go from 0V to +12V. Pin 11 is biased at +0.7V with a resistor and diode so that the signal is detected going above and below +0.7V.

What produces your input signal?

my signal from breaker point
One of these may have somethig to do with your first problem where some leds are on with no input.

Application Hints
Three of the most commonly needed precautions for using
the LM3914 are shown in the first typical application drawing
showing a 0V–5V bar graph meter. The most difficult problem
occurs when large LED currents are being drawn, especially
in bar graph mode. These currents flowing out of the
ground pin cause voltage drops in external wiring, and thus
errors and oscillations. Bringing the return wires from signal
sources, reference ground and bottom of the resistor string
(as illustrated) to a single point very near pin 2 is the best
solution.
Long wires from VLED to LED anode common can cause
oscillations. Depending on the severity of the problem
0.05μF to 2.2μF decoupling capacitors from LED anode
common to pin 2 will damp the circuit. If LED anode line
wiring is inaccessible, often similar decoupling from pin 1 to
pin 2 will be sufficient.
If LED turn ON seems slow (bar mode) or several LEDs light
(dot mode), oscillation or excessive noise is usually the
problem. In cases where proper wiring and bypassing fail to
stop oscillations, V+ voltage at pin 3 is usually below suggested
limits. Expanded scale meter applications may have
one or both ends of the internal voltage divider terminated at
relatively high value resistors. These high-impedance ends
should be bypassed to pin 2 with at least a 0.001μF capacitor,
or up to 0.1μF in noisy environment.
i tried many circuits with different wires but still same problem LED's light

and tried to connect the ic with direst 9V and same problem

used another ic same problem



i will make a video tomorrow to show the problem for you
 
I betcha you built the circuit on a breadboard. The high stray capacitance between all the rows of contacts and between all the wires (that are all over the place) causes the LM3914 to oscillate.
 
I betcha you built the circuit on a breadboard. The high stray capacitance between all the rows of contacts and between all the wires (that are all over the place) causes the LM3914 to oscillate.

i made some changes on the circuit and tried on breadboard and works good

but didn't try it yet on my car

i will try it and give notes and video about it
 
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