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# What this circuit do???

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Hi all
This circuit shown below consists of 6 inverters (NOT gates), that is using the 6 gates in 4069 IC, these gates are connected as shown with 5 resistors, 3 caps and one diode
the o/p is as shown.
can you please tell me what is this o/p.
I think it is an oscillator, but it is very complex to be! I see many oscillators using NOT gates, they use only 2 NOT gates and one cap + 2 R.
What the function of the diode?
thanks very much.
WALID.

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Ok guys, I'll tell you the story
I have a small telephone device, it is very simple, I try to understand its circuit, it contains this circuit in it, this is the 4069 IC.
When I follow the diagram I found that pin 14 of 4069 which is the Vcc of the IC is connected to the phone lines via a cap (1u 250V) and a rectifier bridge and a ripple filter (22u 16V cap) and a zener diode as shown in the circuit below.
The idea is when a ring signal (AC) come into the line it pass through C1, rectified and then regulated through BR1 and ZD1. The resultant DC connected to pin 14 of the 4069 IC which acts as a ringer circuit, the o/p of the ringer is connected to an audio transformer and finally to 100 ohm speaker.
All what I said is clear and simple, the hard thing is the ringer circuit itself, why it appear so complex.
When I connect a 9 VDC directly across the 4069 IC (+ve to pin 14 and -ve to pin 7) I hear like horse sound from the 100-ohm speaker.
Now we all know that the circuit in the fig above is a ringer used in a telephone circuit and the question is: can you please explain it step by step for me.
thanks.
yours
Walid.
NOTE: You can ask me about anything related to what I discuss above.

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Hi Walid,
Inverters 1 and 2 are a Classic Two-inverter Cmos Oscillator operating at about 10Hz.
Inverter 3 is a buffer that drives the 22nF cap.
The diode looks reversed, then it would make a pulsing 10Hz negative voltage.
Inverter 4 is an integrator.
Inverters 5 and 6 are a Schmitt trigger.

I guess the integrator would charge its 47nF cap until its voltage reaches the threshold voltage of the Schmitt trigger which flips the other way. Then the 47nF cap charges the other way and the cycle repeats at the ringing frequency. The pulsing 10Hz gates it on and off so it sounds like a vibrating mechanical ringer.

The transistor provides enough current to drive the transformer which matches the transistor to the speaker.

The cap from the telephone line drives the full-wave bridge rectifier making a supply voltage for the ringer circuit only during ringing.  ;D

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Hi Walid,
Inverters 1 and 2 are a Classic Two-inverter Cmos Oscillator operating at about 10Hz.

how you calculate it (10 Hz)? please it is important.
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To calculate the frequency of a Two-inverter Classic Cmos Oscillator I look at the graph in the book, "CMOS Cookbook" by Don Lancaster. I sketched it here:

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Thank you very very much audioguru, it is helping me very much.
(1) Gates come in two series, 40xx series and 74xx series, I read somewhere that the difference is that 74xx series working on 5vdc only where 40xx series can work up to 18vdc. Is it right?
(2) And also I read that 74xx series are TTL and 74xx series are cmos, I don't sure if this true?
(3) R2 <<< R1 means R1 >= 10 R2 is it ok?
Thank you
Walid

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(1) Gates come in two series, 40xx series and 74xx series, I read somewhere that the difference is that 74xx series working on 5vdc only where 40xx series can work up to 18vdc. Is it right?

Correct, but there is also another Cmos series like the CD4xxx series but it has TTL part numbers and the letter "C" like the 74C04 , which is a CD4069 with the same pins functions as the 7404.
Then there is the high-speed Cmos series which has both TTL and regular Cmos part numbers but with letters "HC" added like the 74HC04 and the 74HC4017. Its operating supply voltage is from 2V to 6V.

(2) And also I read that 74xx series are TTL and 74xx series are cmos, I don't sure if this true?

No, 74xx is TTL. 4xxx, 74Cxx and 74HCxx are Cmos.

(3) R2 <<< R1 means R1 >= 10 R2 is it ok?

R2<<<R1 means that R2 is much less than R1.  ;D
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Please Audioguru tell me how to calculate the freq. of the NAND schmitt in the moisture content detector the first one gate that work as an oscillator
you answered me before abot two inverters oscillatoe
thank you very much power 10000000000000000000000000000000
walid

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Hi Walid,
The 1st NAND gate is converted to an inverter since its other input is always high.
It is difficult to calculate the frequency of a Cmos Schmitt trigger oscillator because they have a wide range of Schmitt trigger threshold voltages and hysteresis and they change with the supply voltage.
You can make 6 variable frequency oscillators from an MC14584 or 74C14 regular hex Cmos Schmitt inverters package with a frequency range of 10:1 by changing the supply voltage from 3V to 18V.

When the output is high, the capacitor charges from the resistor until it reaches the upper Schmitt trigger threshold voltage when the output snaps low. Then the resistor discharges the capacitor until it reaches the lower Schmitt trigger threshold voltage when the output snaps high. ;D

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