Suggestions for a simple system w/ 6 countdown timers, each with a display - Page 1
Forum section: electronics / projects

author: billthebuilder
author_rank: Contributor
timestamp: September 14, 2017, 07:33:34 pm
content: I have a manufacturing station that has 6 items that need to be clamped (de-sta-co clamps) for various durations (~3 to 10 minutes). They will be starting and stopping at staggered times by a technician. I plan to automate the start of each countdown timer with a limit switch on each clamp. I would like each clamp to have a timer display.As of now, I am looking for a timer display module that accepts external input to start the countdown and would beep or ability to send an output signal upon the time running out. I would then sense with the limit switches controlled by an arduino and have that output to each clock.Any better ideas? Any OTS suggestions to make it easier? Also, suggestions for good timer display module that can do what I am asking.I also figured I could buy seven segment displays, some shift registers, and run everything off an arduino but I am not sure if I can have 6 separate countdown clocks all running at once on arduino.Finally, any suggestion for the best way to add a limit switch to a De-sta-co clamp?Thank you in advance,Bill

author: rstofer
author_rank: Super Contributor
timestamp: September 14, 2017, 09:33:55 pm
content: You can have as many displays as you want as long as the displays connect to a serial bus. Like these:https://www.sparkfun.com/products/11629Since you only need 6, you would need 6 chip select outputs plus SPI SCK and MOSI. 9 pins. I prefer SPI over TTL serial or I2C but if these displays are a long distance apart, it might be necessary to use TTL serial and perhaps even convert it to real RS232. Hopefully not.You still have plenty of pins for inputs.I would think about some kind of mount to allow the use of optical switching. Inductive sensing might be too pricey:http://www.cncrouterparts.com/pepperl-fuchs-proximity-sensor-kit-p-293.htmlThese are a lot cheaper:http://cnc-plus.de/en/CNC-Electronics/Switches---Relays/Inductive-Home--and-Limit-Switch--HIGHLY-S17-05P-1--PNP-NO--10-30V-.html

author: sokoloff
author_rank: Super Contributor
timestamp: September 14, 2017, 10:10:39 pm
content: I'd consider a Raspberry Pi and an HDMI monitor with color-coded timers.Color-code the clamps, and put all the display on the monitor.You may have considered and ruled this out already, but if not, it's worth thinking about IMO.

author: billthebuilder
author_rank: Contributor
timestamp: September 14, 2017, 11:11:49 pm
content: We did consider this but figure a simple design with multiple seven-segment LED displays and an arduino will be easier to put together and more suited for our purpose.Thanks though!

author: billthebuilder
author_rank: Contributor
timestamp: September 14, 2017, 11:27:23 pm
content: Thank you! This confirms what I was suspecting we could do and that display is perfect bc I am familiar with SPI and the other display I found only could do I2C.Cheers!

author: Ian.M
author_rank: Super Contributor
timestamp: September 15, 2017, 12:26:22 am
content: If you reject the Pi idea, ATmega238P chips are cheaper than the development time it will take you to implement multiple timers on the same Arduino. You also loose the benefits of scale on the prototype PCB orders - you can get ten boards for negligible extra cost over one. Therefore it makes sense to design a single timer and build six of them rather than trying to hook six displays and inputs to a single Arduino. If one fails, it also minimises the downtime and cost to repair if you have a spare board preassembled.Copy theschematicof an Arduino Mini, (note different pin numbers and loss of A6 and A7 if you use a DIP package ATmega328P) on your own board with whatever input conditioning and display circuits you need. Program the ATmega238P chips with an Arduino bootloader (using an Arduino and the Arduino ISP sketch if you have nothing better), then you can hook up a USB=>logic level serrial adapter and treat your board as if itan Arduino.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: September 15, 2017, 01:52:15 am
content: For finding if they're closed, it's hard to beat a cheap inductive pickup. $16-$20ish from automationdirect.I hate to say it, but unless your development costs are very cheap or this is more than a one-off, it's hard to beat a Koyo-CLICK + CMore micro combo for the controller.EDIT: Keep in mind that requirements always increase once you add automation. The very next thing they'll want is a warning that the wrong clamp has been applied.