I am very new to electronics. New to this board as well.. So please excuse me if my board etiquette is lacking.

I have been given a delay timer circuit that I want to understand, and tinker with. I am very new to electronics and finding that deciphering a phrase or word is key to learning.

Discovering this forum has given me hope that there is a member or members that are sufficiently patient to walk me through this circuit.

The delay timer circuit is a small portion of a PWM motor control circuit. The purpose of the delay timer circuit is to provide a reset signal to a 555 timer so that regardless of the PWM circuit speed control setting, a 100% “Start Up” period occurs when the PWM circuit is turned on.

For the delay circuit:

First I want to understand the interplay of the 5 components and the resulting output of the circuit.

From that I want to experiment with altering the delay time by changing out components.

I look forward to any and all replies, and the learning from those replies.

 

Simple charge up of C6 through R8 causes the delay by setting the reset of the 555 until cap is charged.
Max.

 

Simple charge up of C6 through R8 causes the delay by setting the reset of the 555 until cap is charged.
Max.

Thank you.
Does it follow then that by increasing R8 to some higher value the charge up of C6 will slow thus extending the delay time?

 

hi sparky,
This LTS sim should help you visualise the effect of R1 [timing] value.
E
Note: the 5V supply switch ON, is delayed by 0.1Sec at the start of the plots.

 

Thank you.
Does it follow then that by increasing R8 to some higher value the charge up of C6 will slow thus extending the delay time?

Yes. The circuit depends on the RC constant of the resistor and capacitor pair.

This calculator: https://www.allaboutcircuits.com/tools/555-timer-monostable-circuit/ will help choose components for a monostable version (“one shot”)

This one: https://www.allaboutcircuits.com/tools/555-timer-monostable-circuit/ will help with an astable (oscillator).

 

Thank you!! These are excellent response, and are heading me in the direction of understanding what I'm building and how to tinker with the circuit.
Great!!

 

I am very new to electronics. New to this board as well.

First, welcome to the forum. I, too, have learned a lot here. Knowing you're new to electronics there's something I want to point out just to make sure you understand a little about circuit diagrams. In the two posts @Yaakov linked, you see lines representing the circuit. Where two lines cross it's assumed (in some cases) there is no connection between them. This is especially true when you see two crossing lines that have a larger dot over them, thus indicating a connection. There are a few conventions for drawing circuitry. When I draw a circuit I try to avoid crossing lines because when lines cross - in my illustrations - (or touch) they represent a connection. When I am forced to cross a line that is NOT intended to be a connection I make an arch where one line crosses OVER the other line. It can get confusing to a newbie. If you like I can draw some examples. If you already have that part down then there's no need.

And you'll find that the folks here can be quite helpful AND respectful of others who don't know as much about electronics. These guys are not snobs to nobs.

 

Thanks for the tips Tony. I am aware of the circuit diagram/lines crossing trap. I think I have it mastered now. I'm certain there are a few more "Oops" in my design future.
From all the reading I have done here on AAC, I agree the folks here are helpful and respectful. Very nice!!

 

I have been away from my simple project/learnings as the summer kind of highjacked all my time. Now it is time to settle back into this project and see if I understand the responses.


ericgibbs - Thank you for the LTS sim chart/graph. It has helped me to visualize the delay changes. Are you able to run the same simulation with the 2 microFarad capacitor and a 1000 kiloOhms resistor I mention to Yaakov below?


yaakov - using the monostable calculator I think I see that using a 2 microFarad capacitor and a 1000 kiloOhms resistor the delay will be 2.19 seconds. Am I following the calculator correctly?

Thank you for your help as I get back into this little project.

 

hi sparky,
This is the LTS result with 2uF and 900K 1meg 1.1meg
E

Added a second Sim with longer time base.