#293 CD4060 RC Oscillator

Exploring the behaviour of the CD4060 ripple counter driven by an RC oscillator.

Build

Notes

The CD4060 datasheet describes an RC oscillator configuration for self-driving the ripple counter. A 50% duty cycle is achieved when R1 = R2.

CD4060_rc_oscillator

In this test I’m using R1 = R2 = 10kΩ, and C1 = 1nF. During charge/discharge, the equivalent resistance is 10kΩ|10kΩ i.e. 5kΩ, so the time constant for the rising and falling phases is 5µs (200kHz).

Thus for a near complete charge/discharge of 5 time constants, we’d expect an oscillation of around 40kHz. In practice, I’m measuring 38.7kHz .. so the approximation appears to be pretty close.

Here’s a trace of the oscillator (tapped at the net marked CH2 in the schematic):

scope_oscillator

The reset pin 12 should be pulled low to ensure stable operation. If left floating it can cause spurious results such as picking up 50/60Hz oscillation.

Ripple Counter

The CD4060 is a 14 stage ripple counter constructed of RS flip-flop units - see the functional diagram from the datasheet:

CD4060_functional

The input signal passes 4 stages before the first output is tapped (Q4). Thus the first (Q4) output signal divides the input frequency by a factor of 2^4

Stage 11 (Q11) of the ripple counter is also not exposed on a pin.

The lack of Q0-3 and Q11 is I think just pin economics so it all fits it in a DIP16 package.

The performance is summarised in the table and scope capture below.

Signal	Scope	Frequency (theory)	Frequency (actual)	Note
CH1	CH1	9.765Hz	10Hz	= D7
CH2	CH2	40kHz	38.7kHz	f-input
Q4	D0	2.5kHz	2.5kHz	f-input/2^4
Q5	D1	1.25kHz	1.25KHz	f-input/2^5
Q6	D2	625Hz	623Hz	f-input/2^6
Q7	D3	312.5Hz	312Hz	f-input/2^7
Q8	D4	156.25Hz	155Hz	f-input/2^8
Q9	D5	78.125Hz	78Hz	f-input/2^9
Q10	D6	39.06Hz	39Hz	f-input/2^10
Q12	D7	9.765Hz	10Hz	f-input/2^12
Q13		4.883Hz	5Hz	f-input/2^13
Q14		2.441Hz	2Hz	f-input/2^14

scope_ripple_count

Construction

Breadboard

Schematic