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.

  • 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.

555 timer Monostable mode

Status
Not open for further replies.

WilliamN

New Member
I need a pulse generator that will output a adjustable length pulse(between 1ms to 50ms). I have built a 555 monostable circuit using a 1uf cap for C1 and a 50K pot for R1, this will give me the range I need. I am using this to fire my multistage coilgun. I am using IGBTs for switching the coils. I have a few problems with my circuit though. When I power it up, a few moments later it fires. I have built a photodiode/IRled gate to provide a trigger pulse to the 555. I know that the 555's stable state is when pin2(trigger) is held high. I tried to use a NPN transistor conecting pin 2 to ground, with the pulse from the photodetector gate going to its base. This way when the opto sensor detects the projectile it will send a pulse to the NPN and inturn cause pin 2 to go low. Thats what I thought. The thing fires as soon as I turn it on. Any tips or comments? I am using the basic monostable setup for the 555.
 

k7elp60

Active Member
I assume you have a pull-up resistor from pin2 to Vcc. Try putting a 0.1uF capacitor in parallel with the resistor. On power up the capacitor will look like a short and keep pin 2 high for a moment.
 

D-man

New Member
I have a schematic for a pulse generator curcuit, that works very well, but i have no idea how to post it. If you could tell me how, i can give it to you.
 

donniedj

Banned
I believe this problem is now solve. A PWM IC was mistaken for a 555.
Case closed.
 
Status
Not open for further replies.

Latest threads

Top