Pages: [1]   Go Down
Author Topic: 556 PWM help  (Read 1949 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Newbie
*
Karma: 0
Posts: 24
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I used the following schematic for a 555 (I used 556) controlled pwm circuit, with variable duty cycle (pot).
I looked at the output through an oscilloscope. The pwm works. I am getting the proper duty cycles, but on a DC level (aprox. 6v w/ 6v supply, 1.5v pk to pk). This has happened with other circuits and only with the 556 (555 seems to work fine). I need to use the output to modulate another 555 for IR (reset pin).
Can anyone explain? This is the schematic I used
http://www.josepino.com/circuits/pwm
Logged

Norway
Offline Offline
Sr. Member
****
Karma: 4
Posts: 423
microscopic quantum convulsions of space-time
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

I'm surprised that works at all when using the 555. As far as I can see, the 1k resistor should be between +Vcc (marked +6~9V), and the center tap on the pot. This point should then also be connected to pin 7 of the 555 (discharge. Or the equivalent on the 556).
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 24
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I put up the wrong schematic, here's the one that worked
http://www.instructables.com/id/Simple-and-dirty-Pulse-Width-Modulation-PWM-Wi/#step1
I was taking my output from the output pin and ground. Output has to be taken from discharge and vcc.
Logged

Pages: [1]   Go Up
Jump to: