Handheld Precision Digital Voltage Source - PDVS2mini 20bit

Model: PDVS2mini 20bit
Handmade in Great Britain by Ian Johnston

The PDVS2mini 20bit gives a true 0.00000 to 10.00000Vdc in 10uV steps using a 20bit DAC.
Unlike anything else on the market this is a truly handheld Precision Digital Voltage Source.
With a user adjustable range from a true 0V to 10Vdc and an accuracy/stability down in the uV’s it has a multitude of uses as a calibrator, reference & precision voltage source.

Next batch is in production (available June '23).
Click here to see my Twitter updates for progress, here & here for my YouTube videos.
Apologies for the price increase, the global semiconductor crisis has affected all my supplier costs!

INTRO:

An affordable higher resolution, stable, precision 20-bit voltage source. It supports dual Lithium-Ion batteries c/w charging circuit, 4mm banana sockets and a graphics LCD.

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 potentiometers whatsoever
• 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 (exact colour may vary)
• Atmel Atmega1284 micro-controller
• 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
• Charging pcb/socket for Li-ion batteries using a battery management IC. Batteries and DC adaptor are not supplied
• Battery reverse polarity protection
• Custom CNC'd aluminium anodised enclosure
• UKCA approved

Each unit is assembled & tested in-house, aged/burned-in for 5-7 days and calibrated with a HP3458a 8.5 digit multimeter (Keysight Calibrated).
In the box - 1off PDVS2mini (no batteries, no charger) in an ESD bag, 1off charging cable & Calibration record.

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 = 10mA max.
• Accuracy = Within 50uV. Typically 0.0005% at 10V output
• Stability = 0.00005Vdc variation worst case. 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 graph below of tempco test)
• INL (Integral Non-Linearity) per DAC datasheet = Typical +/- 1bit, Max./Min. = +/- 64bit across 20bit range (however the 11 setpoint system used reduces this considerably)
• Drift (12 months typical) = tba
• 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)
• Charging (external power)  = 18 to 20Vdc.for battery charging, 250mA max. charge current. Uses a 1.4mm Multicomp MP-121WK barrel jack connector, supplied.
• Battery consumption = ~100mA at power up, reducing to ~50mA when LM399AH heater has stabilized (a few minutes)
• Battery quiescent current (unit switched off) = ~4uA.
• Battery = Approx. 12hrs (EBL 600mAh re-chargeable) typical continuous operation
• Dimensions = 105 x 65x 52 mm
• Contains 3D printed & laser cut parts.
• Revised Pcb for 2022.
• Recommended batteries: EBL Li-ion 600mAh via Amazon.com here. Then search on 6F22 (don't order the Usb ones).

MANUAL, DOWNLOADS & FIRMWARE:

• PDVS2mini 20bit Firmware - V1.04 (July 2022) is shipped with all units.
• PDVS2mini 20bit Manual - Version 1.4 (03/07/22) - here.
• Windows PC download here.

RE-CALIBRATION:

The user can re-calibrate the PDVS2mini 20bit via the Calibration menu. The PDVS2mini 20bit uses multi-setpoint X-Y calibration (rather than simple Zero & FSD) in order to help reduce DAC INL (Integral nonlinearity).
Alternatively, you can send your unit back to us for re-calibration, information here.

IMPORTANT NOTE ABOUT BATTERIES & CHARGING:

Batteries are not supplied so customers must supply their own and we highly recommend 600mAH or better Li-ion PP3 batteries from EBC or Etinesan (I did a battery test here). These will give you 12-14hrs continous use between charges.
The batteries used MUST have a built-in protection circuit. I believe most do, but please check if you can.
A DC adaptor or power supply is required (not supplied) to charge the batteries and should be rated at 18V - 20Vdc @ 0.4A. A compatible plug with tails is supplied (centre positive).
Is the charging safe? - I have implemented a current-limited, switch-mode Li+ charger/controller and am running it quite low (0.25A charge current) to avoid any issues. The software also monitors the charge current and can shut it down.
The batteries I recommend have protection circuitry built in as an added layer of protection for under-voltage and over-charging.
Important: The PDVS2mini 20bit is optimized and primarily designed for battery operation, the calibration & stability of the PDVS2mini 20bit is only supported under battery usage. External DC adaptors/PSU's (not supplied) through common mode noise may inhibit accuracy. After a lengthy charging session it is advised to let the PDVS2mini recover (30 - 60mins) in terms of internal heat being generated and any subsequent tempco offset as a result.

PRODUCT REVIEWS (BY OTHERS):

In August 2019 I sent 4 prototype units out to a variety of users in order to gauge response and obtain feedback of both the hardware & software. This proved invaluable as a major software bug was found (and fixed!).
- TiN of volt-nut fame over at XDEVS.COM has done some TEMPCO testing of the PDVS2mini and has published his results including photos here.
- Steve Gardner has published a YouTube review here.
- The DefPom has published a YouTube review here.
- Martin Lorton does an initial 10V test and comparison here.

PHOTOS:

Standard 4mm banana sockets (19mm apart).
1 soft power pushbutton & 5 others for navigating the menus and selecting of the digits for changing the output voltage.
2.4" graphics LCD.
Battery charge socket.
Custom CNC'd aluminium anodised enclosure, new for 2020 and offers better EMI/RFI protection
4 screws allow access to the internals/batteries.

Uses the same microcontroller, charging circuit and DC power circuit as the PDVS2, albeit there's a new 20bit DAC IC.
Shown here is the underside of the PCB with some of the electronic components and the battery holders.

Batteries are easily inserted into their plastic holders.
The DC input and battery charge Pcb is mounted at right angles to the main Pcb.

Practical logging test - Varying temperature between 14 and 34degC (24 nominal) in an environment chamber and recording the output voltage:
Initial value = 9.9999982 Vdc @ 24degC
Max recorded = 10.0000280 Vdc @ 34degC
Min recorded = 9.9999642 Vdc @ 14degC
Yellow = 3458A logging (primary DMM)
Red = Temperature degC
Green = %RH
White = Calculated ppm variation
Results = Typically < 3 ppm variation across a 10degC temperature change, or a tempco average of 0.3ppm/degC.

CUSTOMER COMMENTS:

From Mike in Sweden (Oct. 2019)
"What a great little device you have made! I was impressed by the quality of the PCB and how well put together it is. The soldering is perfect, with all components nicely placed and with perfect fillets on every soldered connection.
I've been doing some testing today with a couple of my good quality meters and my Solartron 7150+ confirmed the accuracy of the device and your calibration. I know my 7150+ reads about 100uV too high, so the readings below are absolutely spot on.
I'm a very pleased customer and thank you for making this device available with such precision for a humane price. I hope you sell lots of them."

MY CUSTOMERS:

Markus from Austria (April 2021):
"I was measuring flicker noise out of a dc amplifier, and the PDVS2mini was used to bias the differential input of the scope so that I could use the highest gain on that channel".

Ross from the USA (June 2020):

Roman from Switzerland (Oct. 2021):
"I am a trained TV / radio electronics technician, electronics technician and ICT engineer and have been dealing with the accuracy of digital multimeters for many years. With the PDVS2mini, Ian Johnsten developed a voltage reference that is unique in this price range - I don't know of any comparable product with this accuracy and stability. The device is produced to a very high quality.
In addition, Ian offers an exceptional service, be it for repairs, calibration, firmware or just for inquiries - you will always be well served. It couldn't be better - great!"