How Shelly UNI works
The world's smallest smart home automation device
If you've landed on this page it means you're trying to understand how the Shelly UNI, the world's smallest smart device capable of automating anything you want, works, then you've come to the right place. You've certainly looked for some reviews to understand how it works, and you've seen that its price is very attractive so you've decided to use it, but you're probably desperately looking for the Shelly uni manual in Italian and can't find it. Well, actually there isn't, so with this article I want to help you with your plans. Perhaps you are looking for the shelly uni schematic to mount it in your intercom or garage, or you want to use the shelly uni's adc and don't know how, or you simply want to use its gpio. In this article I will give a few examples to make it clearer how to use it and how it works. Regardless of whether you want to use it in your motorhome or to switch on the coffee machine or plug it into your home assistant, in this article you will find a guide to using it. The main feature of the shelly uni is the possibility to connect to it in wifi and I have made several videos YouTube to show how it works.
The main features
Operates on both direct current and low-voltage alternating current
It has two output pins to turn on or off whatever you want
It has two inputs capable of checking the status of two different switches to know whether they are on or off
It has a built-in Analog to Digital Converter, capable of converting analogue voltages to numeric format and displaying the value on the Shelly App.
It can manage three temperature sensors, or an integrated temperature and humidity sensor.
Index of Topics
The Shelly UNI device
The Shelly uni is the world's smallest home automation device for making anything we want smart. Its miniaturisation is due to the OEM format, which stands for “Original Equipment Manufacturer”. So it is not a finished product but a small device that we can use in the equipment we want to make. An example is the CamperCheck which uses the Shelly UNI to manage its functionality. Its dimensions are very small at 20x33x13 mm.
Power supply
The Shelly UNI operates at low voltage and can work with either an AC or DC supply. Thanks to this special feature, we can avoid inserting a protective diode against polarity reversal in our circuit; in fact, the Shelly UNI has a diode bridge at its input.
- Operates from 12 to 36 Volts in Continuous
- Operates from 12 to 24 Volts AC
The wifi connection
The main feature of the Shelly UNI is the wifi connection. It is possible to connect to the Shelly in direct way and use it with a common browser thanks to a web page that its internal server provides. Or by giving it Internet access, it is possible to manage its functions remotely. Use is then simplified thanks to the Shelly Cloud App made available free of charge. In addition to the App, Shelly also provides a free Cloud that allows synchronisation of the data collected by the Shelly UNI device and the App downloaded to the mobile phone.
The operating range is up to 50 metres outdoors and up to 30 metres indoors.
The radio signal strength is 1 mW and the radio protocol used is Wi-Fi 802.11 b/g/n on the frequency: 2412 - 2472 МHz (Max. 2483.5MHz)
The Shelly UNI programming connector
The Shelly UNI consists of hardware based on the ESP8266 SOC, which is currently very popular because it is equipped with wi-fi, is inexpensive and is very versatile. Depending on the firmware loaded in this SOC, it is possible to customise its use. On the Shelly UNI there is a connector for reprogramming the ESP8266 chip. If desired, it is therefore possible to load an alternative firmware onto this hardware by overwriting the one provided by Shelly. Online, you can find various alternative firmware such as the Tasmota, ESPurna, ESPHome and others, which are made available free of charge for devices based on these SOCs (such as Sonoff, Shelly and others) in order to add new functionality not provided by the factory. If you want to modify the firmware, there are several guides online that show you how to reprogram the Shelly UNI and customise it to your liking. The photo below shows the pinout of the programming connector.
The Shelly UNI pinout
The Shelly UNI has:
- a power supply pin 1 and pin 2
- an ADC: pin 3
- a sensor bus pin 4 pin 5 and pin 6
- two inputs pin 7 and pin 8
- two outputs: black cables opposite the connector
The Shelly UNI is supplied with a coloured harness that goes on the connector. The colours identify the function of the pins as follows:
For power supply
- Red - 12-36DC
- Black - GND
or
- Black and Red -12-24AC
to follow then
- White - ADC input
- Yellow - VCC 3.3VDC output for sensor
- Blue - Sensor DATA
- Green - internal GND for sensor
- Light brown - Input 1
- Dark brown - Input 2
On the other side of the circuit we find:
- OUT_1 - Maximum current 100mA, AC voltage: 24 V / DC: 36 V.
- OUT_2 - Maximum current 100mA, AC voltage: 24 V / DC: 36 V.
Power Consumption of the Shelly UNI
The consumption of the Shelly UNI is claimed to be less than 1W.
From the tests I carried out, I found that with a DC power supply with a nominal voltage of 12V, there is a consumption of 0.02A, therefore a consumption of 0.24W. In fact the CamperCheck, using the Shelly UNI, can be used on batteries without significantly affecting their charge.
It should be noted that any loads on the outputs do not affect the consumption of the Shelly UNI as they are dry contacts managed by two opto-isolators.
How to use the GPIO of the Shelly UNI
The input pins can accept voltages:
- up to 36V continuous
- up to 24V AC
The use can be to hear a high/low signal, or to recognise an open/closed switch.
According to the type of connection it will be necessary to provide resistors towards the positive of the power supply or towards the negative.
How to use the ADC of the Shelly UNI
ADC refers to an Analog to Digital Converter, i.e. a circuit capable of converting analogue voltages into a digital format. Once the voltage value has been converted into digital format, it is possible to display its numerical value on, for example, the’Shelly App.
The input circuit can convert voltages from 0 to 12V.
Through the App, however, it is possible to enable an input “attenuator” so that voltages from 1 to 30V can be measured. This slightly reduces the accuracy, which is still very high and comparable to that of a mid-range multimeter.
How to measure the battery with the Shelly UNI
The CamperCheck uses the ADC of the Shelly UNI to measuring battery voltage present in the motor home.
It is very important to know that the ADC uses the internal GND as its reference (pin 6, green wire), so if you wish to measure the voltage of the same battery that powers it, it is necessary to bring the internal reference to the reference of the battery itself (pin 2, black wire). To summarise, to measure the voltage of the battery feeding it you need to join pin 2 with pin 6 and then the black wire with the green wire! This explains the trick to getting a correct reading of the ADC. Many people in fact ask themselves: Why does the Shelly UNI misread the battery voltage? The answer is in this paragraph.
How to measure temperature with the Shelly UNI
CamperCheck uses the bus provided by Shelly UNI to measuring temperatures points of interest in the motor home.
Up to three ds 18b20 temperature probes can be connected in parallel on the bus, available on pins 4, 5 and 6.
These allow measurements in a range from -55 to +125 degrees Celsius.
They are also high quality probes with a stainless steel housing that allows use in liquids and aggressive environments.
How to measure humidity with the Shelly UNI
CamperCheck uses the bus provided by Shelly UNI to measuring temperature and humidity at a point of interest in the motor home.
On the bus, available on pins 4, 5 and 6, a DHT22 sensor can be connected.
This has an accuracy of +-0.5Celsius for temperature and +-2%RH (Max +-5%RH) for humidity, a resolution of 0.1Celsius for temperature and 0.1%RH for humidity and a long-term stability of +-0.5%RH/year.
How to reset the Shelly UNI
If you install the Shelly UNI in a network and want to reuse it, you will need to reset it to factory conditions.
If this can be reached from the APP, the reset command can be sent to it, otherwise it can be easily reset via the smd button available between the two outputs as shown in the figure.
To reset the CamperCheck then simply unscrew the two screws holding the container closed and press the easily accessible button.
The Datasheet of the Shelly UNI
In this section I have collected the datasheets and the various documents available.
Universal wifi sensor input - user guide EN
Universal wifi sensor input - Multilanguage user guide
Shelly Cloud App guide EN
Declaration of conformity Shelly Uni EN
Corrigendum
In the datasheet of the Shelly UNI, the position of the channels OUT1 and OUT2 is incorrectly indicated; specifically, the two channels are reversed.
The correct position of the two channels is shown in the figure below.
Thank you very much for the information you have written.very clear
It would also be interesting to know who can mount it and how much it would cost finished, mounted with the temperature sensors, Thank you and by the way great job!
The CamperCheck was created in order to provide the most astute campers with an object that they can install themselves without any great difficulty.
All installation instructions are detailed on the website at this page: https://www.smartcamper.it/installazione/
the cost is 96€ and there are already some workshops that are fitting it to their customers.
Bye!
Thank you for the article, very interesting!
I ended up on this page because I have an elvox 40517 video door phone that uses a 2-wire plus bus and I would like to create scenes with shelly or other devices, which is impossible with the elvox software that only allows you remote and total access from the app (trivially, you cannot create guest access just by opening doors as those who have access with the app can also answer the video door phone). The device is also wifi but there seems to be nothing available to open doors via the web. In short, all I have to do is intercept the signal on the bus and then store it and replicate it when needed. That sounds more or less like what ring intercom does.
Could you help me with the connections and the procedure? If you are close by, I'll invite you for lunch and even pay for your trouble.
Thank you very much
Sorry, I can't help you because we don't do installations.
Excellent article, is there any possibility of measuring the voltage with double digits after the decimal point on a 24v battery’
Of course, up to 30V but the accuracy in my opinion only makes the first digit after the decimal point meaningful.
I need to measure a voltage of about 300 volts DC and via a resistive divider I can make it compatible with the range of shelly uni. However, I would like to display the original value in the app. How can I change the display in the app so that it shows the value of 300 V?
Since the shelly measures up to 30V, the advice I can give you is to make a 1:10 divider, so that a reading of e.g. 25.6V will mean 256V for you and will be quite intuitive.