• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

4046 trouble

Status
Not open for further replies.

confounded

New Member
Hi, i'm using the voltage controlled oscillator of the 4046, i had it working fine the other day, but now i find that the output is stuck on a fixed frequency, determined by the value of the capacitor C1.
I've attached a picture of how i have it connected, when i change the input voltage, no change in output frequency occurs.:confused:
(i'm using resistor and capacitor values between 10k and 1M and above 50pf like the datasheet advises too.)
 

Attachments

audioguru

Well-Known Member
Most Helpful Member
You might have blown up the IC because you have floating inputs. Unused inputs on a Cmos IC must be connected to a voltage that disables them.

EDIT:
Do not connect pin 12 to ground.
 
Last edited:

confounded

New Member
i should of remembered to connect unused inputs! how annoying.
The datasheet says connect R1 and R2 (pins 11 & 12) to Vss (ground) on page 2 why should i not connect it to ground?

Can i also check the input pins to be connected to Vdd are 3 and 14
 

audioguru

Well-Known Member
Most Helpful Member
R2 is used at pin 12 to reduce the frequency range of the VCO and must be more than the value of R1. You shorted pin 12 to ground.
Try the circuit with pin 12 disconnected from ground.
 

Mikebits

Well-Known Member
What are you using for a variable voltage? If it is a power supply, you would want to make sure it is set to 0v before power is applied to the chip, and set to 0v before power is removed from chip, otherwise you might blow the IC.
 

confounded

New Member
yes i am experimenting with an adjustable power supply.

After removing all connections from pin 12 (R2), and tieing all unused inputs to ground, it works! :D

thanks for your help guys
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top