Beginner wanted a delay timer trigger with 555 timer.

Hello everyone!

I have the following scenario.
When a 9v battery is switch on, it waits 5 seconds, then a reed relay is activated.

I am a complete beginner in this so please explain to me as if I'm an idiot.

I only know about capacitor, relays, and diodes at this point.
Am I making any sense?

thank you,

boons

You can use a 555 timer in a monostable mode to get the desired effect. Check out this page, under monostable, and using the circuit modification mentioned in "Power-on reset or trigger" (cap in parallel with power switch)
555 Timer circuits

The basics of why this works is detailed in he Power-on reset section, but the principle is an R-C charging circuit. A series resistor and capacitor can create a voltage-based delay. The resistor slows down how quickly the capacitor can charge up. As the charge in the cap slowly builds, it's voltage rises. When the voltage hits a certain level, you can sense it and use it as a trigger (that's what the 555 timer is doing... sense voltage level and triggers).

An R-C charge circuit will reach 63% of the final voltage within 1 time-constant, which is defined as tau=R*C. So if you have a 5V supply, R=2Meg and C=2.5uF, then the capacitor will reach 63%*5V = 3.15V in tau=2000000*0.0000025 = 5 seconds. I'm assuming the trip-point of the 555 is 3.15V, which should be pretty close. You can pick any value of R & C, and experiment with the length of the delay.

hello there enjunear!
Thanks for your reply. I get very confused when looking at diagrams or schematics. Have you done anything like this before?

maybe helpful
**broken link removed**
**broken link removed**

thanks for your reply ckshivaram!
I've been researching for the past 6-7 hours on data sheets, schematics, diagrams, etc.. but it's all very confusing to me. Is there any tutorials or an easier way to reword all of this for a dummy?
Such as:
Power source connects to 10k resistor. 10k resistor connect to 220uf capacitor. etc...?

boons said:

hello there enjunear!
Thanks for your reply. I get very confused when looking at diagrams or schematics. Have you done anything like this before?

Click to expand...

Quite a few times. These are very simple circuits, so take your time and read about their theory of operation. Think about how the voltage and current change inside the circuits. Some basic circuit element theory wouldn't be bad either... learn how to analyze RLC circuits.

If you wire up the schematic shown with the label "555 monostable circuit with manual trigger", and add a capacitor, as shown in "Power-on reset or trigger circuit", and change the size of the R&C, you should get what you are looking for.

In general: Pick a circuit, build it, and test it. If it doesn't do what you want, grab your oscilloscope and voltmeter to "watch" what the circuit is doing. Use that information to better understand why the circuit works that way, and adjust/modify it... or pick a different design, if it isn't the right type of operation. Trial and error (and analysis) are the best tools to learning electronics.

Hi enjunear,
It's just that whenever I look at schematics, it just looks different from other schematics that this throws me off.
I'm looking to buy this 555 timer from RadioShack, but the numbers from 1-8 are totally different from the schematic. at the monostable you show me.
TLC555/TLC555CP LinCMOS Timer (8-Pin DIP) - RadioShack.com

I'm trying to take my time to read through all the info, but it's just so overwhelming for me

If you could help me read the schematic, it would be wonderful .

boons,

Once the relay is energised, for how long do you want it to stay energised?

Using a delayed trigger to a 555 monostable is ok, but it will hold the relay energised only for the duration of its output pulse.

Hello there Syncopator,

I want to wait 5 seconds then send out the energy, then it will last for another 5 seconds.

Hi

If you want delaye output the 555 should be in astable mode. So let me try to achieve in explaining you or to a layman. The 555 is a timer ic and can be configured in many ways. We will talk about astable mode only here for time being.

555 Timer pin details:
555 timer's power pin is number 8 and ground pin is number 1. There are discharge pin munber 7, Threshold pin number 6, trigger pin number 2. Now ew are left over with 3 pins which are one is control pin number 5 and reset pin number 4. The last is output pin number 3.

Astable mode :
Apply power well within the limits of 555 to number 8. Use a resistor for experiments take a potentiometer say about 10K. Connect one end of 10K to pin 8 and connect center pin to the last pin of 10K and connect the same to pin number 7. Again connect another 10K to this pin and connect center pin to the last pin of 10K and connect the same to pin number 6 and 2. Connect a capacitor say 1uF to pin 2 and ground. Leave pin number 4 and 5 blank. Connnect a LED through a resitor from the power line to the output. Now change the first POT(Potentiometer)connect between pin 8 and 7 slowly you will the change in led on and off. The first POT connected between pins 8 and 7 changes the ON time and second POT connected between pins 7 and 6,2 will change the off time. Ofcourse the changes is more dependent on the capacitor connected to pin number 6,2 and ground.

Now the real stuff. The calculation of on and off can be done as follows.

On time = 0.693 x (POT1 + POT2) x C.
Time in secs, POT values in ohms and C value in uF.
Remember that POT should be minimum 1K or 1000 ohms.

I think this should be clear to you and you can calculate the time you require.

Thankyou

View attachment test1.pdf

Hello there prmurthy!

yes that dummy direction really help. Esp with the pdf. Do you think I can just use pspice to simulate this? I've never use pspice before or any other simulation software, but I heard pspice can be a good tool for simulation.
What do you think?

Use Proteus VSM for simultaion it's easy to use. The above diagram was infact done in Proteus!!

Thankyou

---------- Post added at 18:09 ---------- Previous post was at 18:07 ----------

Follow the link in

https://www.edaboard.com/threads/204446/

This is very good basic electronics simulation in Java.

Thankyou

hello prmurthy,
thanks for the java link. It really helped me out alot! You guys are indeed very resourceful.

I have another questions. Is there such a capacitor that will only discharge when it's full?

If it is helpful I hope atleast you know what you have do ! don't you ??

Now answer to your question. YES the capacitor discharges only when it is fully charged by it's own. The other alternative is manual discharge where you dishcarge by some means.

Hello prmurthy,
OMG I though a capacitor doesn't discharge. I thought when a capacitor fills up, then it stops the flow.
If a capacitor only discharge when it get's full, then can't I just attach like a high Resistor infront of the capacitor and use that as a timer?
Isn't ( ( T = R x C ) / 1000 ) = seconds?

When you require a timer you have use something like capacitor. The value of the capacitor is one which decides the time. Please get into my equation in Deeeeeep.

Hi prmurthy,

Sorry I didn't really understand your last post. What do you mean by "Please get into my equation in Deeeeeep."?