Ian Johnston Engineering PDVS2mini User manual

HANDHELD
PRECISION DIGITAL VOLTAGE SOURCE
Model PDVS2mini
A multitude of uses as a calibrator, reference and
fully adjustable precision voltage source.
Handmade in Great Britain by Ian Johnston
Manual Version 1.0 (19/10/19)
Ian Johnston Engineering Ltd. | www.ianjohnston.com | [email protected]

1
INDEX
FUNCTIONS & FEATURES 2
SPECIFICATION SUMMARY 2
OPERATION OF INSTRUMENT 3
MAIN 5
COMMS 6
SETTINGS 7
CALIBRATION 8
FIRMWARE UPGRADE 9, 10
WINDOWS PC APPLICATION 11
HARDWARE 12
FREQUENTLY ASKED QUESTIONS 13
PRODUCT DISCLAIMER & WARRANTY 14
CE CERTIFICATE & DECLARATION 15
CALIBRATION RECORD (BLANK) 16
The screenshots & photos in this manual may not necessarily 100% reflect the
actual hardware and/or firmware version and are as a guide only.

2
FUNCTIONS & FEATURES
True 0 Vdc to 10 Vdc user adjustable output (5d.p’s, approx. 10uV steps)
Voltage setting via up/down pcb pushbuttons
Soft power switch
Based on the industry standard LM399AH (0.5 ppm/degC) voltage reference
All digital calibration, no internal potentiometers
20bit DAC with an accuracy/stability down in the uV’s (using a PLC filter of 1.0 or higher)
Battery voltage monitor, including low voltage warning, auto-shutdown and charging status
Output voltage monitor including short circuit protection
2.4” Graphics Monochrome LCD (128x64 pixels)
Atmel Atmega1284 micro-controller (uses Arduino bootloader)
Precision chopper op-amp on final output with extra stability achieved using low tempco resistors
Re-calibration by the user possible, and saved to flash rom
Charging pcb/socket for Li-ion batteries using a battery management IC. Batteries and DC adaptor are not
supplied
Battery reverse polarity protection
ABS Hammond enclosure
Manual including factory calibration/settings test record. Unique serial number
CE approved
SPECIFICATION SUMMARY
Voltage reference = Uses an LM399AH (0.5 - 1 ppm/degC temperature coefficient)
0.00000 Vdc to 10.00000 Vdc in 10 uV (0.00001 Vdc) steps
Load = 3kohm minimum. Example: At 10Vdc output with 3kohm load = 3.3mA (whilst maintaining output
within approx. 10uV)
Accuracy = Within 100uV. Typically 0.001% at 10V output
Stability = 0.0001Vdc typical variation. Orientation of the unit may effect output (calibrated horizontally), as will
powering from external DC
Temperature coefficient (unit) = Typically < 3 ppm across a 10degC temperature change (see product
webpage for tempco test)
Drift (12 months typical) = tba - SPEC TO BE CONFIRMED
Stabilization time = 10mins to 1hr depending on ambient temperature, coming off battery charge and last use
Output short circuit = indefinite (20mA)
Power (batteries) = Two Lithium-Ion re-chargeable 9V PP3 batteries (Not supplied, 600mAh batteries
recommended)
Power (external power) = 18 to 24Vdc input (also charges the batteries) @ 400mA min recommended
Battery consumption = 100mA approx. at power up, reducing to 50mA approx. when LM399AH heater has
stabilized (a few minutes)
Battery quiescent current (unit switched off) = 4uA approx.
Battery = Approx. 12hrs (EBL 600mAh re-chargeable batteries) typical continuous operation
Dimensions = 106mm x 66mm x 47mm
Contains 3D printed & laser cut parts.

3
OPERATION OF INSTRUMENT
Power on: Press and hold the power button until the
LCD shows the PDVS2mini splash screen.
Power off: Press and immediately release the power
button. The LCD will clear, power is now off.
The unit will provide a low battery warning at
13.0Vdc and will auto shutdown at 12.5Vdc.
Both settings are adjustable via settings.
Initialize: The splash screen is displayed on power up with the software version before
displaying the MAIN screen. It is recommended to wait 10mins from cold to allow the
LM399AH reference to stabilize.
Menu: To access the MENU, press and hold the ENTER button.
The Main Menu functions are as follows,
UP –MAIN The main output control screen
LEFT –SETTINGS Where user config settings can be changed.
RIGHT –CALIBRATION Where calibration of the unit can be done.
Power source: The primary source of power is the batteries. The best performance of the unit is
when the batteries are being used to supply power without any external power.
External DC input cable wiring: Red +, Blk -.
The battery terminals and the external DC input are reverse polarity protected.
Use only matched charged state batteries, i.e. don’t fit two batteries that are not
charged to the same capacity/level.
The batteries must be capable of charging at a rate of 220mA. Most are, but please
check.
The batteries are charged in-place using the DC socket on the top. The PDVS2mini
must be powered up for charging to take place. This is so the PDVS2mini can
actively monitor the charging process. The batteries won’t charge with the
PDVS2mini turned off.
The unit can be used whilst being powered from the ext. DC socket but with the
following important restrictions/notes:
Minimum DC supply (to charge the batteries): = 18Vdc
Minimum DC supply (no batteries fitted): = 18Vdc
Maximum DC supply: = 24Vdc
Absolute Minimum DC supply: = 14Vdc (unit won’t charge but will run)
Absolute Maximum DC supply: = 24Vdc

4
……cont.
When the batteries are fully charged charging is auto-disabled. To re-enable this
unplug the external DC input and reconnect it, or re-enable “Charge Enable” under
Settings. This is to help avoid trickle charging the Lithium-Ion batteries.
MANUALLY DISABLE CHARGING:
To run the unit off external DC power but without charging the batteries turn off
charging via the SETTINGS menu.
RUNNING WITHOUT BATTERIES FITTED:
To run the unit without any batteries fitted then turn off charging via the SETTINGS
menu. Without this you may get “OVER” on the display.
Please observe the minimum external DC supply voltage.
NOTES:
When running with batteries and also an external DC input the higher voltage of the
two is used to power the unit. Highest voltage wins.
Most Lithium-Ion PP3 batteries have a built in protection circuit and can shut
themselves down if over-discharged. Brands can differ so you may have to adjust the
low battery warning and auto-shutdown voltages accordingly.
On disconnecting the ext. DC socket after fully charging the batteries the battery
voltage should display approx. 16.8Vdc. This is two 8.4V PP3 Li-ion batteries in
series.

5
MAIN
Setting an output: Use the LEFT & RIGHT buttons to select the
digit you want to change then press the UP or
DOWN to change the digit.
The digit selected is indicated with an
underscore underneath.
Output Protection: The voltage monitor detects when the output has been overloaded or subject to a
short circuit. The unit will immediately reduce the output to 0Vc (approx.) and display
an “ERR” message on the LCD. When the problem is resolved the unit will recover
back to normal.
Best Stability: For the most accurate and stable output it is highly recommended to run the unit from
the batteries with no external DC power input. This helps avoids any ground loop
noise entering the system.
Screen Messages: “CHG” - Batteries are charging (also displays the charge current).
“FULL” - Batteries are now fully charged.
“OVER” - The Battery charge current exceeded the maximum allowable.
“OK” - The main voltage output is functioning and is accurate.
“ERR” - An irregularity has been detected on the main voltage output,
e.g. an external short circuit or over-current may have pulled
the output low.
“BT” - Running on Batteries
“DC” - Running on external DC supply
“COMMS” - Serial comms is active

6
COMMS
On power up serial comms defaults to OFF.
The serial comms functionality is an added extra, as such the top acrylic panel must be removed to access
the serial header at the top of the unit. The serial voltage levels are TTL.
To enable comms press and hold the LEFT & RIGHT buttons together. Enabled comms is indicated on the
LCD as well as flashing the small red LED near the comms header..
If the serial comms is not being used then it is advised to leave it switched OFF as it will help the
responsiveness of the unit.
The header on the top of the unit enables direct connection to a Windows PC via a suitable serial to USB
converter, such as 3.3Vdc “Adafruit FTDI Friend”. Not supplied.
Most adaptors will not plug in directly and will need an adaptor cable made up.
PDVS2mini Serial Protocol:
A simple bi-directional Ascii based serial data protocol, BAUD: 250k,N,8,1
Rate = Data from PDVS2mini to PC is sent every 100mS
Format to PC VR0,0,12345
Format from PC <KeyVoltage, 0, 1.23456>
The following details all the data being sent from the PDVS2mini, and only a partial listing of the data from
the PC.
PDVS2mini OUTPUTS TO PC:
KV,0, Output Voltage of PDVS2mini
BV,0, Battery Voltage or DC Input Voltage
BVFM,0, Battery Voltage Feed Mult
OVF,0, Output Voltage Feedback
OVFM,0, Output Voltage Feedback
BC,0, Message = DC Input - Charging, DC Input, DC Input - Full, Running on Batteries, Battery Charge high mA!
BLI,0, Message = Status - Low, Status –Ok
Mode,0, Message = Main Menu, Normal, Calibration, Settings
BMIM,0, Battery Monitor IC Mult
BI,0, Battery current
CMS,0, Cal Mode Sub
dacZ0,0, DAC Zero Cal 0
dacS0,0, DAC Span Cal 0
dacS1,0, DAC Span Cal 1
dacS2,0, DAC Span Cal 2
dacS3,0, DAC Span Cal 3
dacS4,0, DAC Span Cal 4
dacS5,0, DAC Span Cal 5
dacS6,0, DAC Span Cal 6
dacS7,0, DAC Span Cal 7
dacS8,0, DAC Span Cal 8
dacS9,0, DAC Span Cal 9
OUTPUT FROM PC TO PDVS2mini:
<KeyVoltage,0,1.23456> Voltage requested to output from PDVS2mini

7
SETTINGS
User adjustable settings:
Batt Low Indication. Battery voltage at which the unit displays BATTERY LOW.
Batt Low Shutdown Battery voltage at which the unit will auto-shutdown.
Charge Enable Enable / disable battery charging.
This setting is useful when an external DC source is used but the user
doesn’t want the batteries to charge.
Charge Overload mA Charge overload current setting.
The charging circuit is self-contained, but as a safety setting to protect the
batteries & electronics if the charge current goes too high (a faulty battery
perhaps). The charging will be shutdown.
The maximum current should be approx. 250mA, so the default setting here
of 400mA gives some margin.
Charge Full mA Current (mA) at which the battery is determined to be near full.
The charging circuit is self-contained, but as an added extra the software can
shutdown charging if the battery is approaching near full capacity. This is
done by monitoring the charge current and if it drops below a specific level
then the charger is shutdown.
Use the ENTER button to advance through the various entries, and the other buttons to make changes.
See the Calibration record as supplied with your PDVS2mini for the original factory settings.
Any changes to settings are saved to EEprom.
Note: If you decide to make any adjustments to the above settings then please record the original settings
before you start.

8
CALIBRATION
User adjustable / factory calibration:
Use the ENTER button to advance through the 11 point output calibration as well as the other
analogue related calibration, as follows:
Counts: 0.00000 XXXXXXX Counts for 0.00000Vdc output
Counts: 1.00000 XXXXXXX Counts for 1.00000Vdc output
Counts: 2.00000 XXXXXXX Counts for 2.00000Vdc output
Counts: 3.00000 XXXXXXX Counts for 3.00000Vdc output
Counts: 4.00000 XXXXXXX Counts for 4.00000Vdc output
Counts: 5.00000 XXXXXXX Counts for 5.00000Vdc output
Counts: 6.00000 XXXXXXX Counts for 6.00000Vdc output
Counts: 7.00000 XXXXXXX Counts for 7.00000Vdc output
Counts: 8.00000 XXXXXXX Counts for 8.00000Vdc output
Counts: 9.00000 XXXXXXX Counts for 9.00000Vdc output
Counts: 10.00000 XXXXXXX Counts for 10.00000Vdc output
Out.Vdc XX.X XXXX Output monitor counts
Calibration of the output DC voltage monitor.
Batt/DC.Vdc XX.X XXXX Battery / Ext. power supply Vdc Span counts
Calibration of the Battery & external DC supply
for the main screen.
Charge mA XXX XXXX Charge current Span counts
Calibration of the battery charging current monitor.
Use the menu options as detailed at the bottom of the screen to navigate the various entries, and the other
buttons to make changes.
UP/DOWN - 1 count modify
RIGHT/LEFT - 100 count modify for DAC, 10 count for all else
HOLD RIGHT/LEFT - 1000 count modify for DAC, 100 count for all else
See the Calibration record as supplied with your PDVS2mini for the original factory settings.
Any changes to settings are saved to EEprom.
Note: If you decide to make any adjustments to the above settings/calibration then please record the
original settings before you start.

9
PDVS2mini FIRMWARE UPGRADE (ATMEL AVRISP MKII)
Occasionally updated software for both the PDVS2mini and the free Windows app may be available. The
current version numbers/dates will also be published at www.ianjohnston.com, contact us to request the
upgrade files.
The upgrade process I have tested with Win7 & Win10 only, however I cannot guarantee it will work for
you. If the process fails your PDVS2mini may become inoperable until you are able complete the upgrade
process successfully. Important: You do this at your own risk.
Required before you start:
An Atmel AVRISP mkII programmer (USB with 6-pin type header) is req’d.
The data line logic must be set to 3.3Vdc. If you are using a genuine Atmel
AVRISPmkII then set J1 so that the programmer can deliver the correct
3.3Vdc logic levels. Other programmers may vary so please check.
A copy of AVRDUDESS, freely available here:
http://blog.zakkemble.co.uk/avrdudess-a-gui-for-avrdude/
A .HEX file will be supplied for the upgrade.
The current calibration/settings will not be overwritten, but it is advisable to have them written down. Please
refer to the ReadMe.txt file that accompanies the .HEX file for information and any additional instructions.
Procedure:
Remove the 4 screws on the top of the unit, then locate JP1 Power Bypass header and link it out. The
PDVS2mini will switch on. Important: Use batteries only, do not use external DC power.
Connect the AVRISPmkII to the ICSP header on the Pcb. You will
need a 6-pin (2x3) male-to-male header. Note the orientation.
Run AVRDUDESS and make the selections/options as follows:
- Programmer = Atmel AVR ISP mkII
- MCU = ATmega1284
- Port = USB
- Under FLASH locate the new .HEX file
Important!, if the ICSP header is loose in the Pcb then hold it to one side so that all 6 contacts are made.
Press PROGRAM! on AVRDUDESS and the window at the bottom will show you the upload progress and
should complete as shown (<30secs).
That’s it!......disconnect and don’t forget to remove JP1 PWR BYPASS jumper, and re-boot the PDVS2mini.