Model: PDVS2 (new for 2017)
Handmade in Great Britain by Ian Johnston
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.
New for 2017, this is version 2 of the product (PDVS2) and offers the following key features & changes over the original.
Here's a link to the project page containing some tempco tests and other design data, and a link direct to a comparison to other available portable voltage references here. Please note the tests & comparisons were made using the original version 1 (PDVS1) design.
EEVBLOG Starts The Ball Rolling:-
Many thanks to Dave Jones over at the EEVBlog for including an early Version 1 prototype in his Monday Mailbag (I sent him one unannounced!), it looked like it was greatly received! Link to his video here .
So, with the ball rolling I pushed forward with the design even further and have made many improvements over the prototype that Dave Jones saw, as follows:-
Better stability, Less noise on output, Better quality banana sockets, More intuitive user interface, Internal sense line to banana's allowing heavier loads without compromising output voltage accuracy, Coax ditched in favour of heavy gauge wire, MAX6350 Vref ditched in favour of an LM399AH (much better stability and tempco).
Martin Lorton Confirms Hard Work Has Paid Off:-
So, with the new Version 1 unit in production I sent one over to Martin Lorton where he turned out a great independant review of the unit, link to his video here.
But it didn't stop there because not long after in another video Martin used the Voltage Source to help him repair his own HP3458a 8.5 digit multimeter!, see the video here.
Update: Prompted by Martin, I now have my own HP3458a that I use for testing & calibration of all production units.
FUNCTIONS & FEATURES:-
- True 0 Vdc to 10 Vdc user adjustable output in 10 V mode (4d.p’s effective, 38.146uV).
- A 2nd mode offering 0.01 Vdc to 2.0 Vdc user adjustable output (5d.p’s effective, 10 uV).
- Voltage setting or ramp up/down controls via the 12 button numeric keypad.
- Digital Rotary Encoder (potentiometer) allowing quick, on the fly adjustments of the output voltage.
- LED backlighting (user adjustable & auto-limited).
- Soft power switch.
- Based on the industry standard LM399AH (0.5 ppm/degC) voltage reference.
- All digital calibration, no internal potentiometers.
- 18bit 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 overload / short circuit protection.
- 3” 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 via keypad/LCD and saved to flash rom.
- On-board charging added for Li-ion batteries using a battery management IC. Important: Batteries and DC adaptor are not supplied.
- Battery reverse polarity protection.
- Quality Hammond 1599 case.
- Quality aluminium anodized & engraved front panel.
- Quality 4mm banana sockets.
- Printed manual including factory calibration/settings test record supplied. Unique serial number.
- Software function- PLAYBACK mode.
- Software function- RAMP mode.
- Software function- Remote Operation via Windows app (via new USB port). Important: Mini USB cable not supplied.
Prior to shipping each unit:
- Hardware assembled, power-up & tested, all in-house. LM399AH aged/burned-in for 48hrs in unit, including numerous power cycles. Calibrated against an HP3458a 8.5 digit multimeter. Calibrated at approx. 23degC ambient. Packed in a double wall box.
What you get in the box:
- 1off PDVS2 (no batteries, no charger), 1off Charging connector c/w tail, a Calibration record, a CE Declaration of Conformity and details of the PDF manual & Windows app downloads.
- Voltage reference IC = LM399AH (0.5 - 1 ppm/degC temperature coefficient).
- 10 V mode = 0.0000 Vdc to 10.0000 Vdc in 38.146 uV steps.
- 2 V mode = 0.01 Vdc to 2.00000 Vdc in 10uV steps.
- Load = 3kohm minimum. Example: At 10Vdc output with 3kohm load = 3.3mA (whilst maintaining output within approx. 10uV).
- Accuracy = 0.001% (within 100uV & using a PLC filter of 1.0 or higher).
- Stability = 0.0001Vdc variation max. 4d.p. mode.
Stability = 0.00004Vdc typical variation in extended 5d.p. mode.
Drift (long term) = This has not been characterized.
- Temperature coefficient = Less than 1 ppm/degC (tested across a temperature variation of 11.5degC - See project page here for more info).
- Stabilization time = typically 10mins when stored at approx. 23degC. Can be quicker depending on ambient and storage conditions.
- Output short circuit = indefinite (20mA).
- Power Source (batteries) = Two Lithium-Ion re-chargeable 9V PP3 batteries (Not supplied, 600mAh batteries recommended).
- Power Source (external power) = 18 to 24Vdc input (also charges the batteries) @ 400mA min recommended.
- Battery = Approx. 12hrs (EBL 600mAh re-chargeable batteries) typical continuous operation with backlighting off.
- Current drain = 50mA approx. (after 10mins)
- Dimensions = 158mm x 83mm x 35mm (case size).
CURRENT FIRMWARE, SOFTWARE & MANUAL VERSIONS:
PDVS2 Unit - V2.02 - See the PDVS2 Manual below for instructions on how to upgrade.
PDVS2 Windows App - V1.0 - Download here.
PDVS2 Manual - V1.2 (27/04/17) - Download here.
The user can re-calibrate the PDVS2 via the software menu, however, for those that don't have a reference standard to gauge against we offer a return to base recalibration of the PDVS2, the user just needs to pay the shipping in both directions and the service is free.
A 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.
A DC adaptor or power supply is required (not supplied) to charge the batteries and should be rated at 18V - 25Vdc @ 0.4A. A compatible plug with tails is supplied.
Only batteries in a similar state of charge should be fitted together.
Is the charging safe? - We've all seen the issues with phones lately, so I have implemented a well know current-limited, switch-mode Li+ charger/controller and am running it quite low (0.25A charge current - 2.5hrs approx.) to avoid any issues. The software also monitors the charge current and can shut it down.
Finally, the batteries I recommend have protection circuitry built in as an added layer of protection for under-voltage and over-charging.
Note: If the unit is operated whilst charging (via the DC input) additional noise may be incurred on the final output. This is a precision instrument and is designed primarily to be used on batteries.
OPERATION OF INSTRUMENT:-
See the manual for full operating instructions, meanwhile here's a brief rundown:
Press and hold the power button till the LED lights, release the button immediately.
Press and immediately release the power button. The LCD will clear and the LED will turn off.
The unit will provide a low battery warning on the LCD and will auto shutdown.
The menu screen will be displayed on power up. It is recommended to wait 10mins from cold to allow the LM399AH reference to stabilize.
Setting an output (keypad):
Simply type the voltage required using the keypad. Use the ‘*’ key as the d.p., and use the ‘#’ as ENTER (→).
Setting an output (rotary encoder):
Press the rotary encoder to select the digit to be modified.
Rotate the encoder up/down to adjust the digit. Note: rotating the digit above it's single figure will roll to the next significant digit, i.e. 7, 8, 9 will then roll to 10, 11, 12 etc.
10V / 2V modes:
The 10V mode has 4 full d.p.’s and an extra 5th, i.e. X.XXXXx, that’s 100uV minimum step changes, and 38.146uV steps on the 5th.
The 2V mode has 5 full d.p.'s i.e. X.XXXXX, that's 10uV minimum step changes.
The user can set up 5 voltages that can be played back one after another over time. Each one of the 5 has a time in seconds associated with it. The playback can be looped.
The user can set up 5 voltages that can be played back over time, the unit ramps up or down to the next voltage in the queue. Each one of the 5 has a time in seconds associated with it. The playback can be looped. Output refresh is approx. 200mS per change.
By connecting to the USB port of a Windows PC (FTDI drivers loaded) the PDVS2 can be remotely controlled.
The V2 unit is visually pretty close to the previous version except of course for the rotary encoder, the USB port and the charging port visible on the side.
Internal view of the new unit. A brand new V2.0 pcb which includes a new, bigger, processor.
A new banana plug adaptor board.
A DC adaptor jack next to the batteries to power the unit from an external source and/or charge the batteries. You can see the charger Pcb under where the batteries sit.
The banana adaptor pcb. This tidies up the interface from the main Pcb to the banana sockets. The 3 connections are voltage out, 0Vdc and a v.sense line. In this photo you can also see the backlighing module (white) under the LCD.
Naked view of the pcb's top side. Here you can see the battery charging circuit below keyboard (not shown) and well out of the way of the main pcb. You can also see the rotary shaft encoder and on/off switch below the Lcd.
Naked view of the pcb's bottom side. The LM399AH voltage reference (large white package) stands out and the PP3 battery terminals. At the top of the photo you can see the mini Usb connector and the DC power connector. Over to the left is the Atmega1284 uController.
Screenshots (subject to change relative to firmware updates):
The main menu screen. You can also see the backlighting in operation.
Main screen - 10v mode.
Main screen - 2v mode. The 5th DP is now full size as 10uV resolution is attainable in this mode.
Calibration Screen. DAC calibration and other analogue cal. The 2V mode is calibrated independantly from the 10V mode.
PLAYBACK mode running.
RAMP mode running.
Windows Application - Remote operation and monitoring of the PDVS2 on Win7/Win10.
Remotely set output voltages by way of the SET OUTPUT data entry, or use the slider control.
Most functions, settings and calibration can be done via the application. Comms is FTDI via USB.