## Precision Voltage Reference

Precsion 5 Volt Reference & Precision Resistance. For instrument testing and circuit design. Available both assembled and in DIY kits
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38 backers pledged \$1,132 to help bring this project to life.

Replay with sound

# Precision Low Voltage Reference

What is a precision low voltage reference?

It is a device that can supply a precise voltage, usually at least .1% accurate. For 5 volts, this would be +/- .005Volts or between 4.995 to 5.005 volts.

Is it the same as a 5 volt power supply?

No, both may supply 5 volts, the precision reference does not supply the same amount of current. It may only be good for a few milliamps. This is not enough to charge your iPhone, but it can supply the reference voltage to an ADC.

How does it work?

Our precision reference uses the band gap principle. See below for more details on how this works.

What do you do with a precision reference?

We have used ours to check the accuracy of our voltmeter. While not a calibration grade piece of equipment, it should be accurate enough for most home and hobby use.

These can be used in test equipment and oscilloscopes because of their precise nature. They can also be used for a precise analog reference to an analog-to-digital (ADC) input on a microcontroller.

For our device, we chose the highest available voltage of 5 Volts. We could have easily gone with a 3.3V, or a 2.5V version, and it would have been easier. Instead we added a voltage divider cicuit with 0.1% precision resistors to provide an additional voltage reference.

The voltage divider used with precision resistors provides another test for your voltmeter. You can test your voltmeter against the precision resistors to confirm the accuracy of your resistance readings.

The combination of precision voltage and precision resistance gives you a precision current reference. If you connect your voltmeter in line with the voltage divider, then you will get a precision amperage to measure.

Here is a video of the Precision Voltage Reference being used to test a cheap multimeter from Habor Freight.

https://youtu.be/yPi0Hh5jwW0

# Why two different versions?

While designing and testing our prototype voltage reference, we found that the volyage reference chip required a narrow range of input voltage between 5.3 – 5.5V supply. If we provided less, the voltage reference wasn’t accurate.

We had two good options on how to supply power in this narrow range. The simple solution was to provide 6 volts using two 3V batteries, then use a diode to step down the voltage. This is a simple and reliable design if you use fresh batteries. Around this simple approach we built the basic board.

We like simple, but keeping fresh batteries is hard. Our first Kickstarter campaign was a power supply that provided a constant 5 volts power over a wide range of incoming voltage. We checked the data sheets and found that the voltage booster could be adjusted to supply up to 5.5 volts. If we added the boost voltage circuit, then it won’t matter if the batteries are not fresh. As an extra bonus, we could get the correct output voltage with just a single 3V cell battery.

All rewards ship without batteries.

If you want to get more than one reward, you simply increase your pledge amount to include the extra rewards. Please add an extra \$1 for each additional reward you want. We will ask during the survey about which rewards you pledged to support.

# What is the difficulty level?

The DIY kits do require soldering. We would estimate about medium difficulty with hand soldering. The difficulty is with the small parts. You need a fine tip soldering iron, tweezers, and a steady hand. Once you have one side tacked down it is very easy to solder the other side.

We include a paper stencil for appling the solder paste. This is for oven or hot plate soldering. Oven soldering is supper easy, but you still need tweezers, and a steady hand to position the parts.

A used toaster oven is easy to find for this purpose. It does need to heat to 250 C or 500 F. Please do not use the same one you use for cooking.

# Special International Version

With the rapid increase of shipping costs, we are going to offer a modified kit that will ship international flat rate. This means there are no parts more than ¼” thick (6mm) and no tracking on the package. This is the lowest price shipping we could find.

# The Band Gap Principle

https://en.wikipedia.org/wiki/Bandgap_voltage_reference A circuit is built using p-n junctions is such a way as to result in a voltage that is between 1.2-1.3 volts depending on the design. This is close to the theoretical 1.22 eV of silicon at 0 kelvin. Several such circuits can then be combined to create a larger voltage difference. While some circuit design allow for calibration to improve the accuracy, other devices have an intrinsic precision. The voltage reference we use has a maximum temperature drift of 5 ppm/°C.

### Risks and challenges

The biggest challenge is the pricing. The parts used are high precision and are more expensive than typical parts. This makes it diffucult to achieve an attactive price. We have to stay focused on design and function.

The next biggest challenge is the increase cost of international shipping. The price has more than doubled in the last few years. We will continue searching for options.

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### Combo - Advanced Voltage Ref

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