Portsdown DMM Display and Logger - Revision history

G8GKQ: /* Modification of the DMM */

2025-11-04T15:31:26Z

Modification of the DMM

G4FRE at 11:14, 8 October 2025

2025-10-08T11:14:38Z

G4FRE at 11:13, 8 October 2025

2025-10-08T11:13:21Z

G8GKQ at 10:18, 29 July 2023

2023-07-29T10:18:28Z

G8GKQ: /* Modification of the DMM */

2023-07-29T10:17:28Z

Modification of the DMM

G8GKQ at 17:21, 2 January 2023

2023-01-02T17:21:55Z

G8GKQ: /* Running Plot */

2023-01-02T17:21:26Z

Running Plot

G8GKQ at 17:18, 2 January 2023

2023-01-02T17:18:58Z

G8GKQ at 17:15, 2 January 2023

2023-01-02T17:15:01Z

G8GKQ: /* Battery Capacity */

2023-01-02T17:13:23Z

Battery Capacity

← Older revision		Revision as of 15:31, 4 November 2025
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	Other opto-isolators can be used - mine was sourced from the junk box. If the opto-isolator has lower gain, the 4k7 between the transistor base and the +3 volt supply may need to be increased to 10k.		Other opto-isolators can be used - mine was sourced from the junk box. If the opto-isolator has lower gain, the 4k7 between the transistor base and the +3 volt supply may need to be increased to 10k.
		+
		+	Note that the Portsdown 5 uses GPIO pin 18 for the DMM input as opposed to GPIO pin 3 on the Portsdown 4.

	The amplifier transistor (BC108 or any medium-high gain npn) was required because GPIO pin 3 on the Raspberry Pi is intended for use with i2c, and I was unable to disable the internal pullup. This results in the input signal to the GPIO pin being idle = mark = data 1 = 0v, and start bit = space = data 0 = +3.3v. The serial data is 2400 baud, inverted serial signals. This can be decoded by selecting "Serial Pol Inverted" from the "More Settings" menu and restarting the application.		The amplifier transistor (BC108 or any medium-high gain npn) was required because GPIO pin 3 on the Raspberry Pi is intended for use with i2c, and I was unable to disable the internal pullup. This results in the input signal to the GPIO pin being idle = mark = data 1 = 0v, and start bit = space = data 0 = +3.3v. The serial data is 2400 baud, inverted serial signals. This can be decoded by selecting "Serial Pol Inverted" from the "More Settings" menu and restarting the application.

@@ Line 18: / Line 18: @@
 Other opto-isolators can be used - mine was sourced from the junk box.  If the opto-isolator has lower gain, the 4k7 between the transistor base and the +3 volt supply may need to be increased to 10k.
-The amplifier transistor (BC108 or any medium-high gain npn) was required because GPIO pin 3 on the Raspberry Pi is intended for use with i2c, and I was unable to disable the internal pullup.  This results in the input signal to the GPIO pin being idle = mark = data 1 = 0v, and start bit = space = data 0 = +3.3v.  The serial data is 2400 baud.  Inverted serial signals (as provided by the circuit above) can be decoded by selecting "Serial Pol Inverted" from the "More Settings" menu and restarting the application.
+The amplifier transistor (BC108 or any medium-high gain npn) was required because GPIO pin 3 on the Raspberry Pi is intended for use with i2c, and I was unable to disable the internal pullup.  This results in the input signal to the GPIO pin being idle = mark = data 1 = 0v, and start bit = space = data 0 = +3.3v.  The serial data is 2400 baud, inverted serial signals. This can be decoded by selecting "Serial Pol Inverted" from the "More Settings" menu and restarting the application.
 A battery capacity testing application is described below that monitors (and plots) the voltage of a rechargeable battery and disconnects the load when it reaches a preset "discharged" voltage.  The relay for disconnecting the load is be operated from the Raspberry Pi pin 26 (GPIO 7).  This is the same pin as is used for switching the Noise Source in the NF Meter, and is found on pin 7 of the Portsdown 25-way interface connector.

@@ Line 16: / Line 16: @@
 [[File:Interface Circuit.jpg|800px]]
-Other opto-isolators can be used - mine was sourced from the junk box.  If the opto-isolator has lower gain, the 4k7 between the transistor base and the +5 volt supply may need to be increased to 10k.
+Other opto-isolators can be used - mine was sourced from the junk box.  If the opto-isolator has lower gain, the 4k7 between the transistor base and the +3 volt supply may need to be increased to 10k.
-The amplifier transistor (BC108 or any medium-high gain npn) was required because GPIO pin 3 on the Raspberry Pi is intended for use with i2c, and I was unable to disable the internal pullup.  This results in the input signal to the GPIO pin being idle = mark = data 1 = 0v, and start bit = space = data 0 = +3.3v.  The serial data is 2400 baud.  Inverted serial signals can be decoded by selecting "Serial Pol Inverted" from the "More Settings" menu and restarting the application.
+The amplifier transistor (BC108 or any medium-high gain npn) was required because GPIO pin 3 on the Raspberry Pi is intended for use with i2c, and I was unable to disable the internal pullup.  This results in the input signal to the GPIO pin being idle = mark = data 1 = 0v, and start bit = space = data 0 = +3.3v.  The serial data is 2400 baud.  Inverted serial signals (as provided by the circuit above) can be decoded by selecting "Serial Pol Inverted" from the "More Settings" menu and restarting the application.
 A battery capacity testing application is described below that monitors (and plots) the voltage of a rechargeable battery and disconnects the load when it reaches a preset "discharged" voltage.  The relay for disconnecting the load is be operated from the Raspberry Pi pin 26 (GPIO 7).  This is the same pin as is used for switching the Noise Source in the NF Meter, and is found on pin 7 of the Portsdown 25-way interface connector.
@@ Line 30: / Line 30: @@
 Note that the screen image is also available on the web interface, but no control is possible - that must be done from the touchscreen.
-The Parkside Meter has a "Battery Save" function that turns the meter off after 15 minutes.  To disable this for long duration testing, press and hold the red "Select" button whilst initially turning the meter on.  The small "power" symbol in the very top left of the display will be occulted to show that the Power Save funtion is not activated.  Battery life in this mode is estimated at 400 hours or so.
+The Parkside Meter has a "Battery Save" function that turns the meter off after 15 minutes.  To disable this for long duration testing, press and hold the red "Select" button whilst initially turning the meter on.  The small "power" symbol in the very top left of the display will be turned off to show that the Power Save funtion is not activated.  Battery life in this mode is estimated at 400 hours or so.
 ====Large Number DMM Display====

@@ Line 16: / Line 16: @@
 [[File:Interface Circuit.jpg|800px]]
-Other opto-isolators can be used - mine was sourced from the junk box.  If the opto-isolator has lower gain, the 4K7 between the transistor base abd the +5 volt supply may need to be increased to 10k.
+Other opto-isolators can be used - mine was sourced from the junk box.  If the opto-isolator has lower gain, the 4k7 between the transistor base and the +5 volt supply may need to be increased to 10k.
 The amplifier transistor (BC108 or any medium-high gain npn) was required because GPIO pin 3 on the Raspberry Pi is intended for use with i2c, and I was unable to disable the internal pullup.  This results in the input signal to the GPIO pin being idle = mark = data 1 = 0v, and start bit = space = data 0 = +3.3v.  The serial data is 2400 baud.  Inverted serial signals can be decoded by selecting "Serial Pol Inverted" from the "More Settings" menu and restarting the application.

@@ Line 16: / Line 16: @@
 [[File:Interface Circuit.jpg|800px]]
-Other opto-isolators can be used - mine was sourced from the junk box.
+Other opto-isolators can be used - mine was sourced from the junk box.  If the opto-isolator has lower gain, the 4K7 between the transistor base abd the +5 volt supply may need to be increased to 10k.
 The amplifier transistor (BC108 or any medium-high gain npn) was required because GPIO pin 3 on the Raspberry Pi is intended for use with i2c, and I was unable to disable the internal pullup.  This results in the input signal to the GPIO pin being idle = mark = data 1 = 0v, and start bit = space = data 0 = +3.3v.  The serial data is 2400 baud.  Inverted serial signals can be decoded by selecting "Serial Pol Inverted" from the "More Settings" menu and restarting the application.

← Older revision		Revision as of 17:21, 2 January 2023
Line 1:		Line 1:
−	The Portsdown Digital Multimeter display and logger works with a modified Parkside PDM300 C3 multimeter (seasonally available for £11.99 from Lidl) to display and log the meter readings. It is selected from Menu 2, Test ~~Equipemnt~~, DMM Display.	+	The Portsdown Digital Multimeter display and logger works with a modified Parkside PDM300 C3 multimeter (seasonally available for £11.99 from Lidl) to display and log the meter readings. It is selected from Menu 2, Test Equipment, DMM Display.

	[[File:PDM 300 C3.jpg\|100px]]		[[File:PDM 300 C3.jpg\|100px]]

@@ Line 46: / Line 46: @@
 The time span of the plot can also be selected from the Settings Menu.  Selecting "Plot Span Minutes" also allows selection of the most detailed span - 1 pixel per sample.  The Parkside meter takes a sample about every 800 ms.
-The "More Settings" menu allows selection of a single-span mode, selection of an alternate DMM Type (not yet implemented), slection of a reversed polarity serial input, and editing the Title line displayed at the botton of the graph.
+The "More Settings" menu allows selection of a single-span mode, selection of an alternate DMM Type (the Maplin/Precision Gold N56FU - not yet implemented), selection of a reversed polarity serial input, and editing the Title line displayed at the botton of the graph.
 A .csv file of the last 501 readings can be saved by pressing the "Save .csv File" button on the "Actions" menu.  The file is saved in the /home/pi/snaps folder on the SD Card.

← Older revision		Revision as of 17:18, 2 January 2023
Line 1:		Line 1:
−	The Portsdown Digital Multimeter display and logger works with a modified Parkside PDM300 C3 multimeter (seasonally available for £11.99 from Lidl) to display and log the meter readings.	+	The Portsdown Digital Multimeter display and logger works with a modified Parkside PDM300 C3 multimeter (seasonally available for £11.99 from Lidl) to display and log the meter readings. It is selected from Menu 2, Test Equipemnt, DMM Display.

	[[File:PDM 300 C3.jpg\|100px]]		[[File:PDM 300 C3.jpg\|100px]]

@@ Line 20: / Line 20: @@
 The amplifier transistor (BC108 or any medium-high gain npn) was required because GPIO pin 3 on the Raspberry Pi is intended for use with i2c, and I was unable to disable the internal pullup.  This results in the input signal to the GPIO pin being idle = mark = data 1 = 0v, and start bit = space = data 0 = +3.3v.  The serial data is 2400 baud.  Inverted serial signals can be decoded by selecting "Serial Pol Inverted" from the "More Settings" menu and restarting the application.
-A battery capacity testing application is being developed that will monitor (and plot) the voltage of a rechargeable battery and disconnect the load when it reaches a preset "discharged" voltage.  The relay for disconnecting the load will be operated from the Raspberry Pi pin 26 (GPIO 7).  This is the same pin as is used for switching the Noise Source in the NF Meter, and is found on pin 7 of the Portsdown 25-way interface connector.
+A battery capacity testing application is described below that monitors (and plots) the voltage of a rechargeable battery and disconnects the load when it reaches a preset "discharged" voltage.  The relay for disconnecting the load is be operated from the Raspberry Pi pin 26 (GPIO 7).  This is the same pin as is used for switching the Noise Source in the NF Meter, and is found on pin 7 of the Portsdown 25-way interface connector.
 ===Use with Portsdown===

← Older revision		Revision as of 17:13, 2 January 2023
Line 70:		Line 70:

	When the measured voltage reaches the previously set Discharge voltage, the load will be turned off, the plot stopped, and a screenshot (snap) of the screen stored in the /home/pi/snaps folder. Note that if the voltage falls to anything less than 0.5v, the test is not immediately terminated as this is unlikely to have been caused by a normal discharge and is probably a connection issue!		When the measured voltage reaches the previously set Discharge voltage, the load will be turned off, the plot stopped, and a screenshot (snap) of the screen stored in the /home/pi/snaps folder. Note that if the voltage falls to anything less than 0.5v, the test is not immediately terminated as this is unlikely to have been caused by a normal discharge and is probably a connection issue!
		+
		+	A .csv file of the discharge voltage can be saved by pressing the button on the Actions Menu.