Difficulty with LM567

[obrien136]

Hello,

I am trying to get an LM567 to respond to an output from a 555 timer in the astable mode. The R1 and C1 for the LM567 are 10Kohms and 6.1uF. The other components are the same as on the data sheet in the drawing with the multiple tome decoders (I'm just using one of these tone decoder circuits). I may have damaged the LM567 because the voltage I measured on the input was about 8VRMS which would give a peak voltage higher than the max tolerable on that pin. I lowered the voltage with a voltage divider but there was still 6 VRMS on the input although the divider output was 1VRMS. I don't know why. I don't have a scope. The LM567 output doesn't go low for any frequency in the range the 555 was set for. See schematic below.

George

**broken link removed**

 

[BradtheRad]

The initial post seems to be gone even though I saw it here an hour ago.

I experimented with the 567 IC some years ago. It is fussy about your incoming signal. It must go above and below certain volt levels, in order to be detected. I forget if it needs to cross 0V. Schematics have a capacitor at the input pin, to convert the input to AC.

You reported reading several volts on the input pin, even with nothing connected. This is after it was exposed to 8V.

Guidelines usually say you should not subject an input to a greater amplitude than the supply rails. There is a chance this caused the internal circuitry to create a low impedance between the input pin and the supply pin. It may have ruined your 567 chip.

However on the possibility it did not, you may succeed in making it work, by making certain that the incoming signal has sufficient amplitude to activate the internal PLL. You'll need an oscilloscope to measure this, or perhaps an ingenious meter circuit consisting of led's which light at certain threshold levels.