
After seeing several other voltage reference projects online and many more assembled boards on Ebay, I decided to put together my own version of a multi-output module that I could use for prototyping ADC, and other projects.
I needed at least a 2.048 volt and a 4.096 volt precision reference. An extremely high accuracy 5.000 volt reference was also on my list. I already had an enclosure on hand that I wanted to use, but in my early mock ups the three outputs on the front panel just didn’t look right. So for good measure a 2.500 volt reference was added to the project.
The 4.096 volt and lower reference IC’s only required a stable 5 volt supply, but the 5.000 volt reference IC required a minimum of 9 volts and preferably 10 volts for maximum stability. So a separate add-on board was designed to supply 9 or 10 volts along with a warm-up timer and battery low voltage alert.
All the voltage reference IC’s are produced by Maxim Integrated.
The 5.000 volt reference is a MAX6350, and is a low-noise, precision voltage reference with an extremely low, 0.5ppm/°C typical temperature coefficient and ±0.02% initial accuracy.
The three lower voltage references are all MAX6126A series ultra-low-noise, high-precision, low-dropout voltage references, that feature high-stability, laser-trimmed, thin-film resistors that result in 3ppm/°C (max) temperature coefficients and ±0.02% (max) initial accuracy.Quad voltage reference board fabricated by OSH Park
Eagle schematic for Quad Vref board
Quad Vref board layout in Eagle
Board with solder paste and components placed
Vref board after solder reflow. Had a couple of capacitors that didn’t straighten out as much as I had hoped, but no issues other than looks.
Eagle schematic for power and status monitor board
Power and status board layout in Eagle CAD
Shared project Power & Monitor board on OSH Park
This board connects the two 6 volt AAA battery packs in series. and also has connections for the front panel “On” switch. There are jumpers for selecting 9 or 10 volt supply output for the 5.000 volt reference. I included both so I could test the difference in stability between the two, as the specifications from Maxim lead me to believe the 10 volt power would give a typical Line Regulation of 2 ppm/V vs 10 ppm/V for a lower voltage.
An Atmel Tiny85 processor turns a LED from red to blue after 120 seconds has elapsed from power on, and also monitors that the batteries are supplying a minimum of 10.5 volts to the regulators. If the voltage drops below the threshold, the front panel LED blinks red at a 1 pps rate to indicate low battery.
Atmel Atiny85 Arduino code:
// Precision Reference Standard // 2016 Greg Christenson (Barbouri) // Dual LED driver for system warmup and battery 5V Ref 12volt battery low voltage // LED is solid red upon power on for 2 minutes then switches to solid blue after 2 min. timeout // If 12 volt battery goes below 10.5 volts then LED flashes red one time per second for 1/10th second int BlueLED = 4; // Blue LED resistor and Anode int RedLED = 3; // Red LED resistor and Anode int Voltage = 1; // Battery voltage from divider R3, R4 - 1/3 of 12 volts nominal Analog pin1 int val=0; // Setup variable val for analog read unsigned long time; // Setup variable for time as unsigned long to read milliseconds void setup() { // Set pin locations pinMode(BlueLED, OUTPUT); // sets the digital pin as output pinMode(RedLED, OUTPUT); // sets the digital pin as output digitalWrite(RedLED, LOW); digitalWrite(BlueLED, LOW); } void loop() { // Check current conditions time = millis(); // read current time from power up val = analogRead(Voltage); // read current battery voltage if (val <= 715) // 1/3rd of 10.5 volts * 0.0049 volts per unit (5 V ref) { digitalWrite(BlueLED, LOW); // Turn off Blue LED if 2 min. timeout has elapsed digitalWrite(RedLED, HIGH); // sets the Red LED on delay(100); // keeps the Red LED on for 0.1 seconds digitalWrite(RedLED, LOW); // sets the Red LED off } else if (time < 120000) // Check for warm-up time { digitalWrite(RedLED, HIGH); // sets the Red LED on until 2 min. timeout } else { digitalWrite(RedLED, LOW); // sets the Red LED off digitalWrite(BlueLED, HIGH); // sets the Blue LED on } delay(900); // keeps the Red LED off for 0.9 seconds or delays loop }


The Maxim MAX6126A IC’s have the capability of Output and Ground sense leads which I connected to the front panel terminals.
Also used were wideband noise reduction capacitors on the NR pin of the IC’s.
I also utilized 10μF conductive polymer solid electrolytic chip capacitors for the output bypass capacitors.
Ferrite toroid cores were placed on all banana jacks, along with ferrite bead cores on all force and sense wires to reduce EMI.

I used “Front Panel Designer” to layout the front panel, and the file was sent to Front Panel Express for production. Panel thickness is 1.5 mm and is black anodized aluminum.
The monitor LED is connected to the panel using a fiber optic light pipe.

I also tested using my Fluke bench meter and all outputs were well within the stated initial voltage accuracy. I had included connections on the circuit board for adding an external trim potentiometer to the 5.000 volt reference, but currently do not see the need to implement it. I will monitor the drift with ageing and add if needed in the future.
Link to EagleCAD schematic and board files download
Link to Front Panel Designer panel files for use with Hammond 1455N1202 box
An updated version of the Voltage Reference Quad Project:
Voltage Reference Quad Project Version 2 – Part 1
thank for sharing, I will try to build one.
can you give the ic3 reference please on Power & Monitor board
IC3 on the power and status monitor board is a 78L05 regulator in a TO-92 package. It supplies a regulated 5 volts to the TINY85 IC and LED.
Thank again, I realise, I did not have ferrite toroid cores. I quickly check on ebay but I did not found. do you have a reference of your ferrites ?
I just completed the pcb soldering. I will also order the same box as you propose is a nice design.
Hi nechry,
I used both:
399–10822-ND B‑20L-44 FERRITE BEAD CORE EMI 1.6MM
on the force and sense connections, and
399–10876-ND ESD-R-12S FERRITE TOROID CORE EMI 7MM
on each of the jacks, from Digikey.
is possible to add a picture of the jacks, see from internal. I did not realise you put also some at this place.
So I order everything form digikey, box and ferrites
And Still remain a question:
The Four output voltage board is powered with J1 from Power & Monitor board (5ref+/5ref-) but the other side +9Batt comme also from the Power & Monitor board ? of a 9v battery ?
And last think in picture the batteries holder seem twice 6xAAA but you wrote about 6V battery pack. if I’m correct 6x1.5 = 9V but 2 in packs in series will result 18. and the Power & Monitor board supposed to get maximum of 12V. so I’m little bit confuse for powering the 2 boards.
Sorry if my question same to be, too basic.
Hi nechry,
The best picture of the internal jacks is labeled “Lots of Teflon wires running to the front panel”. The ferrite toroid’s are held in place by the yellow kapton tape, and are just the right size to slide over the extra threaded part of the jacks. The ferrites are not mandatory, just an extra layer of noise protection.
The 6 cell AA battery (9V) pack powers the three MAX6126A Vref’s only (-BATT +9BATT) and is switched separately from the first side of the double pole front panel power switch.
The MAX6350 is powered by regulated 9 or 10 volts thru J1 from the “Power and Status” board using two separate 4 cell AAA (6V) packs connected in series thru the board for 12 volts total.
There is a separate connection on the “Power and Status” board that connects to the second side of the double pole front panel power switch.
Thank Barbouri for explanation, I’m previously thinking the “Power and Status” board monitor the entire Voltage Reference IC not just the 5V. I thinking to only use a 12V battery pack for the “Power and Status” board and also the +9Bat with the 12V to. With this, all forth ref are monitored. Do you have a reason to separate and only monitor a battery pack?