Hi

I need to design a 30 second delayed counter circuit. The spec is after a output (0) is given this said circuit will count down 30 seconds and then turn a transistor on which in turn turns 4 reed switches on. The transistor / latch and reed switch part is all completed.
The problem i have is the delay

Firstly I choose a 555 timer only to discover the delay in monostable was the oppersite to what I need.

So then I decided to go astable, only to be completely baffled by setting the clock pulses to 1 sec intervals.. I tried to use and online calculator and have the following as R1 R2 & C

R1 = 2k
R2 = 72k
C = 10 microfarad


So in believing i had this sorted i went for a dual 4 bit binary counter. By linking these two together, I can get a count of 30 secs.

I have run this through the crap bit of ecad software and I get pulse of 500ma out of output of the timer but the counters do not work. I am using a program called multisim....

I have spent some serious hours on this now and quess i stupid..

Sorry for the long first post but can anyone help me

Cheeers

SI

 

Well I spent another couple of hours today and I now have the counters working in ecad.. Hooray.....

All the leds flash and count to 30..... Can someone please help with the maths etc so I know excactly what R1 and R2 ans C are please as i still think its running quick.


Finally,, I know i have to really rest the counters prior to clocking the count, where should I connect the rest pins on the counters to. I am sure I have read somewhere that they can be connected to the trigger or pin 7, to give a low, prior to the 555 starting its oscillating...

Anyone please....

Cheers

Si

 

Find the datasheet for the 555 timer. Go to application circuits for astable and a set of equations will be listed. You should set your capacitance to 10uF since capacitances are usually hard to match in design equations. You will be left with 2 equations and 2 unknowns (R1 and R2). If you are still stuck, post again.

 

Did you do a search for 555 in this forum or in Google?

There have been many posts in this forum on the over used 555.

I just did a search for 555 in this forum and found 159 hits.

__________________
Len

 

Ok guys can any help further please. I now think I have a counter circuit, but im still having problems big time.

The 555 is astable and counts 30seconds through the dual 4-bit counter.

Basically I then need the output to turn the transistor on, and turn on S2 (this is gonna be a reed switch which is not in the design package so just used a switch) S1 again is a reed switch which latches S2 until the reset switch is de-pressed.

problems i have is cause i need a 30 count, delayed i could not use monostable. But using astable the counter is always on. I will have an input from an optocoupler which i want to trigger the counter device.

Also I have no idea how to connect the reset to the counters.

Am i barkin up the wrong tree with this whole design. ?

Also my output to the transistor is only a 1 sec pulse, does this matter to turn it on to turn on the reed switches

Once the reed switches are latched id doesnot make any difference to what the circuit is doing, unless there is another signal from the optocoupler.

Please help I have lost the will to live at the moment

 

I have attached the print screen too

The dual timer is a 74393, then outputs go to a 8input nand, through a invertor to the transistor bp108.

Attached Images

Image2.jpg (181.6 KB, 16 views)

 

hi,

I would suggest that you place the J2 reed sw in the collector circuit of Q2, in series with LED9, connect the emitter to 0V.

Which is the RESET button?

Why didnt you choose a 555 pulse rate that gives an high output U3B/8 at a 30sec interval, it would remove the gate driving the opto.

A 1sec pulse more than enough to operate a reed sw.

Is the opto shown with all its connections?

I cannot see any decoupling capacitors on the circuit?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

If I am reading your schematics correctly, there is a wiring error in your 555. Pin 6 should be connected directly to pin two so it can discharge through R2. This will improve your timing output.

__________________
All those who believe in psycho kinesis, raise my hand.

 

There are to reset switches in the circuit.

1. is clear the counter prior to the count comenceing

2. the reset for the latched reed switch, which holds the other reed switch on

 

Sorry but I really think you are. I would start over again with a different idea.
There are easier ways to get a 30m second delay.

 

Thanks for all the input guys.....

I have finally managed to sort the whole circuit....

thanks again

 

How? Inquiring minds would love to know.

__________________
All those who believe in psycho kinesis, raise my hand.

 

I will post up circuit diagram tomorrow, when I get a chance, however here is a brief explanation.

The problem with the reset/clr for the binary counters.
As I have an opto isolater as my interface, the reset have been held high unless i get input from the device this circuit is for. Ie a low. As the 555 is astable and constantly running, the counters are released and counting comences.

With requards the transistor etc.
The output from the counter goes into a binary latch/flipflop. Once the count reaches 30, the 1 sec pulse, turns Q to a high. This turns on my 4 coil relays and as the enable on the flipflop is held by a further n/c coil relay, the the other 4 relays are now latched. There is a pushbutton switch on the enable pin to reset the flip/flop, which in turn resets the 4 coil relays.

I hope I have explained it well enough. Like I said I will post a diagram tomorrow.. And again thanks for all your help guys

Si