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Please forgive my bad language.

I am making a vehicle speed indicator with an LM2917N-14 frequency-to-voltage convertor (datasheet). I tried it with a cheap XR2206 function generator and an NE555 variable square wave.

With the NE555, the LM2917 is working properly, the output voltage follows the input frequency (even though 5 V supply NE555). However, with XR2206 in both sine and square wave there is no DC output on LM2917 even using a 12 V supply for the XR2206.

At first I thought the XR2206 output had to be buffered/amplified before it was fed to the LM2917, but it still didn't work. (I use simple TLC2272 op-amp as a buffer/amplifier.)

The XR2206 itself is normal, has a frequency and DC out of sine and square wave (I measured it with DMM because I don't have an oscilloscope).

My question is why can't the XR2206 drive the LM2917? What should be added so that the XR2206 can drive the LM2917?

I really hope the answers, Thank you .....

enter image description here

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The 555-based signal generator very probably has an output which goes down to almost 0 V.

With a 12 V supply, the output of the XR2206 function generator will be centred around 6 V.

Here is an oscilloscope display showing what you are working with:

Output signal of an XR2206 at 440 Hz showing numerical statistics

The yellow "1" marker on the left is at 0 V. The vertical scale is 2 V/div. I set it to show all the measurements.

Looking at the datasheet for the LM2917N-14, it seems to me that you need a 10 kΩ, or maybe 15 kΩ, resistor instead of the 1N4148 diode, so that it makes a voltage divider to raise the switching threshold for the LM2917 to a sufficently high voltage.

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    \$\begingroup\$ Hi Andrew ..... Thanks you for your advice .... I will try with a variable resistor and I'll let you know the results later ....... \$\endgroup\$ – Dul Joni Aug 14 at 12:28
  • \$\begingroup\$ @DulJoni Yes, that worked. It is a bit different for new users to the site as they have to wait some times for some things. Glad the answer worked for you :) \$\endgroup\$ – Andrew Morton Aug 14 at 15:21
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I have tried it according to the attached image and it works perfectly both sine and square wave. Thank you very much for your advice and lessons ..... God bless you.......

enter image description here

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