ThermoPiggy - Revision history

NebarnixWikiSysop at 05:48, 3 August 2020

2020-08-03T05:48:47Z

NebarnixWikiSysop: /* Arduino */

2020-08-03T05:40:31Z

Arduino

NebarnixWikiSysop: /* Arduino */

2020-08-03T05:40:00Z

Arduino

NebarnixWikiSysop at 05:36, 3 August 2020

2020-08-03T05:36:51Z

NebarnixWikiSysop: /* Interface */

2020-08-03T05:11:44Z

Interface

NebarnixWikiSysop at 05:08, 3 August 2020

2020-08-03T05:08:41Z

NebarnixWikiSysop: /* XH-B310 Overview */

2020-07-14T04:45:08Z

XH-B310 Overview

NebarnixWikiSysop at 19:04, 9 July 2020

2020-07-09T19:04:53Z

NebarnixWikiSysop: New Page

2020-07-09T03:28:46Z

New Page

New page

==Problem Statement==
The XH-B310 is an inexpensive and wonderful temperature display. It can be powered from 12V or a 9V battery, and displays the K-type thermocouple temperature on a large LED display. The best part is that they can ready up to 800 degrees C! These are super useful for keeping an eye on a reflow oven temperature, or a distillation or liquid temperature during chemistry experiments and so on. The possibilities are really endless. It is also, oddly, cheaper than a thermocouple IC breakout board several times over.

Unfortunately the developers did not think to provide the temperature data to the user in any sort of easily digestible form. Using these to feed data into a smarter system is unfortunately not so easy. This is truly disheartening as the system uses an STM8 micro-controller, which could easily provide temperature data at 9600 baud on a spare pin.

==System Overview==
It should be possible to piggy-back an arduino nano onto the analog signals output by the various sensors to the board's ADC. This is not as ideal as just getting the result from the micro for many reasons, but it does mean it is entirely possible, and indeed quite likely, that each board will display a slightly different reading. This will have to be acceptable...

==XH-B310 Overview==
The XH-B310 is a clever design and can be broken down into the following components:

# 5V Regulator - To provide a constant voltage to the LEDs
# 3.3V Regulator - Powers the rest of the board
# op-amp - 76x gain stage for thermocouple voltage
# analog mux - to act as a high impedance buffer for the thermocouple? Maybe there are other designs with more than one thermcouple? Still seems strange to devote so much board space to a part that isn't even really used.
# 2.5V precision reference for the ADC
# 10k thermistor to sense ambient temperature
# a diode for reverse polarity protection
# An stm8s003f3 microcontroller

@@ Line 27: / Line 27: @@
 === Cold Junction ===
-The ambient temperature of the cold junction is measured using a thermistor.
+The ambient temperature of the cold junction is measured using a 10k glass packaged thermistor. Since there is no part number on the thermistor, the beta value was determined experimentally and found to be ~4050.
 === Process Junction ===
@@ Line 35: / Line 35: @@
 The solution here is to either discard point that differ greatly (or maybe just require several in a row to change the alert status of the setpoint being reached or reset) or even better would be to intercept the MUX control signal, and use it to our advantage.
 == Arduino ==
@@ Line 43: / Line 44: @@
 The source code can be found here: https://github.com/nebarnix/XH-B310_Backpack

@@ Line 39: / Line 39: @@
 [[File:ThermoPiggy_bb.png|left|800px]]
+<br clear="all"/>
 An Arduino nano was used due to the low cost and high availability.
 The source code can be found here: https://github.com/nebarnix/XH-B310_Backpack

@@ Line 38: / Line 38: @@
 == Arduino ==
-[[File:ThermoPiggy_bb.png]]
+[[File:ThermoPiggy_bb.png|left|800px]]
 An Arduino nano was used due to the low cost and high availability.
 The source code can be found here: https://github.com/nebarnix/XH-B310_Backpack

@@ Line 24: / Line 24: @@
 <br clear="all" />
 ==Interface==
 === Cold Junction ===
@@ Line 34: / Line 35: @@
 The solution here is to either discard point that differ greatly (or maybe just require several in a row to change the alert status of the setpoint being reached or reset) or even better would be to intercept the MUX control signal, and use it to our advantage.

← Older revision		Revision as of 05:11, 3 August 2020
Line 22:		Line 22:
	To calibrate the offset voltage, the unit pulses the MUX every 67 seconds for a little over a second and reads the negative pin of the thermocouple.		To calibrate the offset voltage, the unit pulses the MUX every 67 seconds for a little over a second and reads the negative pin of the thermocouple.

		+	<br clear="all" />
	==Interface==		==Interface==

@@ Line 14: / Line 14: @@
 # 3.3V Regulator - Powers the rest of the board
 # op-amp - 76x gain stage for thermocouple voltage
-# analog mux - to act as a high impedance buffer for the thermocouple? Maybe there are other designs with more than one thermcouple? Still seems strange to devote so much board space to a part that isn't even really used.
+# analog mux - which switches between passing the + (for normal operation) and reading the - (for calibration)
 # 2.5V precision reference for the ADC
 # 10k thermistor to sense ambient temperature
@@ Line 20: / Line 20: @@
 # An stm8s003f3 microcontroller
-For reasons not fully understood, the unit pulses the MUX every 67 seconds, which results in a dropout. The behavior still needs to be analyzed with an O-scope to understand the purpose (perhaps it is a calibration pulse?)
+To calibrate the offset voltage, the unit pulses the MUX every 67 seconds for a little over a second and reads the negative pin of the thermocouple.

← Older revision		Revision as of 04:45, 14 July 2020
Line 19:		Line 19:
	# a diode for reverse polarity protection		# a diode for reverse polarity protection
	# An stm8s003f3 microcontroller		# An stm8s003f3 microcontroller
		+
		+	For reasons not fully understood, the unit pulses the MUX every 67 seconds, which results in a dropout. The behavior still needs to be analyzed with an O-scope to understand the purpose (perhaps it is a calibration pulse?)

← Older revision		Revision as of 19:04, 9 July 2020
Line 8:		Line 8:

	==XH-B310 Overview==		==XH-B310 Overview==
		+	[[File:XH-B310_Front.jpg\|400px\|thumb\|right\|Back of the unit]][[File:XH-B310_Back.JPG\|400px\|thumb\|right\|Front of the unit, LED display removed]]
	The XH-B310 is a clever design and can be broken down into the following components:		The XH-B310 is a clever design and can be broken down into the following components: