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I want to do a project where the temperature of a device is controlled by toggling on/off a heating element (120VAC),presumeably by using a relay. I would like a board that has an input for a temperature sensor of some sort and some form of a display and buttons to allow me to create a user interface.

Whether the board itself has the relay or not does not matter (I can use 5V to trigger a 'powerswitch tail' if I need to). The board would definitely need a display of some sort (nothing fancy needed), some buttons, and the ability to measure temperature accurately (+/0 0.5 °F worst case). Does anybody know of anything that fits the bill?

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I've seen a couple of "buttons and LCD and thermocouple" kits. If none of them are adequate for what you are working on, I suspect you could pick almost any "buttons and LCD" kit and almost any "thermocouple interface kit" and connect them. (in no particular order):

== buttons and LCD and thermocouple ==

== buttons and LCD ==

== thermocouple interfaces ==

If you ever need to measure temperatures above 125 C (257 F), you'll need to use a thermocouple and a thermocouple interface chip. (Thermistors and IC sensors such as the Analog Devices AD592 and the Maxim DS18B20 cost less, but generally can't handle temperatures above 125 C).

(I've made this "community wiki" so others can add really good/cheap examples and trim out obsolete items).

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Those who know me realise I am biased towards the Arduino way of doing things, so if you had an Arduino, HD44780-compatible LCD, Analog Devices TMP36, that powerswitch tail from Adafruit, the job could be done very easily.

You might find this article of interest, it discusses how to use that temperature sensor, LCDs and making decisions based on temperature.

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All the parts would be relatively easy to get and put together: LCD module, any simple MCU, some suitable digital temperature sensor, buttons... and the relay should indeed be easy to control. I think this complete DIY approach would seem most obvious and you won't "waste" a kit doing it.

If you want to look for a ready board, something with enough PIO, ISP, some sync serial bus for the sensor and ready buttons and displays would probably be. Maybe some available memory for logging and/or UART in case you want to attach it to a computer at some point. Which particular one probably depends on which one you can get and from where.

I'd probably pick an ATTiny series AVR and a separate LCD module, some stripboard, and pin headers and work from there.

Either way, I don't think trying to fit the sensor and/or relay (that needs to have one half well isolated) on the same board is a good idea unless you have a really good reason for it.

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My design (Eagle files and Arduino sketch) is on the web:

http://dorkbotpdx.org/blog/scott_d/temperature_controller_board_final_design

The design includes an Arduino compatible and has provision for a MAX6675 thermocouple chip and an IR temperature sensor based on a modified IR thermometer from Harbor Freight Tools. It also has a built in interface for a common 16x2 (or similar) LCD, inputs which could be used for buttons (although I'm currently using an encoder instead) and a digital output for controlling an SSR or other relay. A number of local hobbyists are using this board for temperature control of various projects including reflow hotplates.

I note that you require +/- 0.5°F temperature accuracy, which is better than most thermocouples can provide, so you might have to find some other type of temperature sensor for your project. It depends on the temperature range you need to measure.

If you want to use my Eagle files to make a PCB, I can recommend the Portland DorkBot group PCB order: http://dorkbotpdx.org/wiki/pcb_order. It is inexpensive and designed for hobbyists.

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