Hi friends,
I’m working on a project that requires a digital countdown timer that can be preset for a fixed duration (e.g., 60 seconds) and is triggered by a 4-20mA input signal from an I/O module. Ideally, the timer would:

• Start a visible count down when the signal is active
• Reset automatically if the signal drops before the countdown finishes
• Trigger an output or alarm if the full countdown completes
• Be DIN-rail mountable or otherwise integrable into a control panel (but not necessary)

Does anyone have recommendations for timers that can do this?
Thank you!

 

Whats the maximum duration?

 

Looks like a job for a 555-timer circuit.

 

If I read correctly the OP wants a digital readout. That complicates things a bit (1 chip vs. 7-8).

 

more details needed...

4-20mA is commonly used as analog signal.

 

Welcome to AAC.

Sounds like you need a PLC.

 

Whats the maximum duration?

Hi Wendy, the maximum duration is 10 minutes.

 

Do you want a digital (numerical) display or what (a bargraph for example)?

 

Do you want a digital (numerical) display or what (a bargraph for example)?

Yes, I do. I apologize for the lack of detail. I want it to be numerical digital countdown. I'm hoping for a decent size one. between 8" and 24". It should be very visible to the tech workers who will be monitoring the amount of time they have to complete their tasks. (The purpose of the timer is because our technicians are working with delicate material which cannot be exposed to ambient temps for too long. The timer is there to keep them on track)

 

Digital displays between 8" and 24". That's a tall order!

 

How advanced are you in electronics? A PIC is a programmable device which is a also a microprocessor design for control application in industrial electronics programming cost much less than parts. I tend to be a discrete component girl, basically 'cause I'm not smart enough to program PICs.

 

You won't find something off-the-shelf for this need. Here's a slightly modified one that I made a couple of years back with an added current loop input (was originally -1 to +1v in for a lab experiment).

It uses an OLED display, but could easily be modded to drive a 8" flapper panel, or a row of 4 NEOPIXEL panels, though not sure how the menu/set function would work. How had you envisaged setting the timeout, sensitivity, etc.? As its all done in software.

It wouldn't be hard to rework it for a DIN rail mount (probably not needed if with display) and 24v or 110/240AC power input

 

Again the programming is (for me) the issue I can help with the giant display, but not much more.

 

Just design big digits yourself... Or .. make the segments out of pieces of led strips.. or just get ready made led matrix....

 

definately sounds like a job for a jellybean plc and an off the shelf lcd display. maybe an lcd with a trigger and use an opto isolator to trigger the lcd to start counting down? The loop power should be more than enough to trigger the opto

 

There is way too much information missing here! As already mentioned. 4-20mA is an analog current loop format signal. So what value will be needed to start the sequence?? How repeatable will that trigger point need to be?? 4-20 mA is seldom an ON/OFF mode signal in the normal world.
SO "Y" is right!! A PLC with one analog current loop input and a 16 output module to feed a the large two digit display.
The count down can be easily done with ladder logic and COMPARE commands, and an internal counter.

BUT the whole concept is doomed because the workers will be distracted by watching the count down.