Electric Timer With a Micro-Controller

Question

I am trying to replace some electric timers with some sort of a micro-controller based solution http://www.directindustry.com/industrial-manufacturer/panel-mount-timer-154503.html. I would like to run at least 10 timers from one micro-controller, a 20x4 LCD and 4 push buttons. All these requires 38 pins (I think I counted it right). The LCD will display the timers set value. Since there are 10 timers I though a 20x4 will be ideal. The push buttons will be used to set the time. The timers will be independent from each other.

I was planning to use a PIC16F887A micro-controller but I released that the number of pins are not sufficient. An Arduino Mega would be ideal but forums suggested that it is not reliable for an industrial application. What other micro-controllers are out there for this sort of application.

The current timers has 24V inputs and 24V outputs. How can address this issue?

I am new to this micro-controller business and PCB designing. I've been trying to learn on the internet so some links would be really helpful, specially for programming.

Also, do you guys think replacing those timers with a micro-controller is a good idea?

Thanks a bunch.

Answer 1

Personally, I'd try to create a general purpose module by using small boards and relays and put them into a larger plastic box. For a microcontroller, I'd use something like this solution. http://www.cnx-software.com/2015/01/18/one-dollar-development-board/ This is a $1 stm8s board. It'll do pretty much what you want from a controller standpoint. You'll need to get an SDLINK debug interface which you can get for about $5, but you can use that on STM32 boards too. You can also get low cost STM32 minimal ARM boards for under $4, which will have much more Flash and RAM, but for simple timing functions you only need the STM8S. This would be an example of the STM32 board you could get cheap... http://www.ebay.com/itm/STM32F103C8T6-ARM-STM32-Minimum-System-Development-Board-Module-For-Arduino-M2-/221982023431?hash=item33af28df07:g:BU0AAOSwKtlWhJmi

That being said, you will then need some kind of relay board to work with the higher voltages. All the MCU boards will run from either 5V or 3.3V. None of these CPUs will be able to handle any serious amount of industrial current. You will need a relay board. It could be done using semiconductors too like SCR's or power transistors or something, but the easiest and most reliable way to do it is to use relays. Some kind of board like this one could handle 10A, 250V, etc, etc.. http://www.ebay.com/itm/8-Channel-DC-5V-Relay-Module-Board-for-Arduino-Raspberry-Pi-DSP-AVR-PIC-ARM-/201400438757?hash=item2ee466cfe5:g:JMYAAOSw9N1VwDSM Based on the panel meter examples you provided, I'd could use a calibrated potentiometer and use the ADC on either STM8S or STM32 board to read the voltage and use that to set the time value. Alternatively you could hook up a cheap LCD and a keypad to enter it digitally. With the more complex one, you might want to use the STM32 rather than the STM8S. For all these boards if you search around you can find the lowest price. That kind of relay board could be had for about $10. I'd say your most important step is your initial research into how you want to put it together and the features you want..i.e. your design. Your lowest cost solution is to use a calibrated potentiometer with no LCD to specify the time. The most expensive would be to have an LCD or LED display and possibly showing the time counting down. Remember the more complex your user interface, the higher the price. Finally, don't forget that someone else may already have done this. You can get a simple panel timer for under $10 already...like this one. http://www.ebay.com/itm/Panel-Mounted-Type-110V-AC-5A-8-Pin-DPDT-60s-Power-On-Delay-Time-Relay-Timer-/271425503741?hash=item3f323881fd:g:gsoAAOSw~gRVidjM ...or here is an even cooler solution for even less money... http://www.ebay.com/itm/DC-12V-Multifunction-Self-lock-Relay-PLC-Cycle-Timer-Module-Delay-Time-Switch-/271958222133?hash=item3f51f92535:g:hnYAAOSwhcJWLiuB

Good Luck and remember to let us know what you finally ended up doing.

Answer 2

Some remarks:

• If this is a one-off, buying 24 simple timers might be cheaper.
• an AVR being mentioned as not being suited for industrial work was likely due to Atmels not-perfect record of being able to deliver. For a one-off this has no relevance.
• whether a uC-product is suited for industrial use depends mostly on the curcuit around the uC, not on the uC itself.
• if you need more I/O, consider I/O extenders (I like MCP23017).
• the 16F877 was once THE PIC to pic, but that time has passed. There are better ones now, consider at least a 40-pin 18F chip. (But personally I would go for a Cortex chip).