HX711 module VCC and no VDD

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Hi,

 

Circuit

 

I am trying to build the above circuit powered by battery alone. Sparkfun HX711 is expensive and hence I am using Amazon HX711

 

HX711 module has Operating Voltage: 2.7V to 5VDC and Operating current: <10 mA

 

Sparkfun HX711 has VCC and VDD. VCC is the analog voltage to power the load cell. VDD is the digital supply voltage used to set the logic level. In many cases, you can just short VCC and VDD together. If your microcontroller uses 3.3V logic however, you'll want to connect VCC to 5V and VDD to 3.3V.

 

Amazon HX711 has only VCC and no VDD. Therefore, can I connect LoadCellHX711SF VCC to NodeMCU1 3V3 instead of connecting LoadCellHX711SF VDD to NodeMCU1 3V3?

 

Thanks and regards,

Rashmi

 

Last Edited: Sat. Dec 7, 2019 - 07:28 PM
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Wrong Community, wrong Forum.  MAybe you should look at what Google has to offer in examples by simply typing HX711 in the search bar

 

I'll move this to general electronics.

 

Jim

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Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Welcome to the Forum.

 

Full disclosure: I've not used this chip.

 

I also can't see the "Circuit" you linked to. 

It would be easier if you embedded the circuit schematic into your post.

(Click on the "mountain range" icon, three to the left of the smilie face icon, to post a jpg image.)

 

The HX711 has THREE (+) power supply pins:

VSup      V supply, input to the on chip voltage regulator, 2.7 - 5.5 V

AVdd      Analog supply V+, 2.6 - 5.5 V

DVdd     Digital supply V+, 2.6 - 5.5 V

 

DVdd need to be the same voltage as the micro the chip is connected to.

If you are powering the micro at 3.3 V then connect DVdd to the same 3.3 V power supply V+ rail.

 

It would appear that the "Generic Amazon HX711" PCB uses only a single V+ pin.

So presumably on the PCB AVdd is directly connected to DVdd, the separate on-chip analog voltage regulator is actually not being used, and its Vsup is also connected to the AVdd and DVdd V+ rails.

The Vfb pin should be connected to Ground.

 

You should be able to follow the traces on your PCB and verify the above connections.

 

The benefit of this is that the connections are simple, there is a single V+ and a single Ground for the board.

 

The down side of that configuration  is that the analog circuitry is subjected to the electrical noise on the digital V+ and Digital Ground power rails.  Running the 24 bit ADCs on 5 V, (i.e. NOT the 3.3 V the micro is running at), might also improved the system's noise performance at small signal levels.  To see that difference one would need a very carefully designed PCB, power supply, and by-pass cap management.

 

So, bottom line, with the board you have, YES, you can connect the PCB's V+ to the same power supply as the micro, (3.3 V).

 

(I think that is what you were asking about.)

 

JC 

 

Edit: Typo

Last Edited: Sat. Dec 7, 2019 - 08:14 PM
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Hi,

 

Circuit is as shown below

 

https://cdn.sparkfun.com/assets/learn_tutorials/5/4/6/SparkFun_HX711_Load_Cell.pdf shows that VDD is DVDD and VCC is VSUP (as shown below)

 

 

Generic Amazon HX711 module shown below has VSUP and DVDD shorted

I want to use the Amazon HX711 module as it is cheaper. Can I connect VCC of Amazon HX711 module to 3.3V output of the nodemcu esp32 wroom 32s development board?

 

Thanks and regards,

Rashmi

Last Edited: Sat. Mar 14, 2020 - 09:32 PM
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There should be plenty of examples online.

Your 9V battery won’t last very long - the esp32 can be very hungry and you’re wasting 2/3 of your battery power as heat.

Last Edited: Fri. Mar 13, 2020 - 10:20 PM
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Not trying to be snarky, but, in this case, it seems to fit.

 

There is an old saying: You get what you pay for!

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Apropos of the HX711 - investigated it, rejected it. There is a little known but occasionally available range of similar chips from Chipsea - we use the CS1238 as a superior replacement for the HX711; it's not only two thirds' of the price (from the factory) but it offers two channels at all gain options. The B channel on the HX711 doesn't offer the same gain range as the A channel, which strikes me as a very silly design decision...

 

I was also unimpressed with the only (at the time) Arduino driver software, which appeared to be written by someone who hadn't actually read the data sheet correctly. </rant>

 

https://lcsc.com/product-detail/... (the datasheet linked is in Chinese with occasional English bits; I managed to write drivers for it (sorry, they're company property so I can't publish them) before I managed to locate an English version with only occasional recourse to google translate).

 

One thing to remember on these types of chips is make sure that the Vdd supplied to the chip is the same as the voltage supplied to the strain gauge. The ADC is ratiometric, and so is the strain gauge, so changes (noise) in the supply are applied equally to the measurer and the measured. Sticking five volts on the sensor and three volts on the chip will work, but not as well as it could. Though you do need to ensure that the power rail is sufficiently smoothed/regulated to be below the noise level you need to achieve. You're trying to measure a handful of nanovolts at the highest gains here... which you will need to get sane results from that sensor.

 

Neil

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"...Amazon HX711 has only VCC and no VDD. Therefore, can I connect LoadCellHX711SF VCC to NodeMCU1 3V3 instead of connecting LoadCellHX711SF VDD to NodeMCU1 3V3? "

 

Yes. However, the NodeMCU1 will make it impossible to use a battery in this circuit, because it uses 200 mA during boot and WiFi operation.

 

Why are you using a NodeMCU1 as the CPU?  As a simple small weight-measuring scale, the device is too small to justify implementing a WiFi interface.

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Simonetta wrote:

However, the NodeMCU1 will make it impossible to use a battery in this circuit, because it uses 200 mA during boot and WiFi operation.

 

Why are you using a NodeMCU1 as the CPU?  As a simple small weight-measuring scale, the device is too small to justify implementing a WiFi interface.

I have changed the circuit to use 4 load cells which will be connected to one HX711 module. I am planning to measure weights for two types of ranges (200g-2kg, 3kg-25kg).

I am using NodeMCU ESP32 WROOM 32S(30pin) development board. Which is the best way to power this board?

I want to use a CPU which has both WiFi, Bluetooth and OTA. I choose this one as it is popular for such requirements. Which CPU would you recommend?

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Those are all nice "requirements". But what about others, such as battery power, cost, size, and such? You MAY have requirements that are mutually incompatible. If so, then you need to decide which ones really are requirements.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

Last Edited: Sun. Mar 15, 2020 - 11:27 PM
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And there Jim has it in a basket... cost vs function vs power. Saving a buck on production costs keeps management happy; adding functionality keeps sales happy; making a set of batteries last six months instead of six weeks keeps the customer happy. Sometimes these aims are mutually exclusive.

 

Neil

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I am planning to use nodemcu esp32 30 pin development board. I need to use Vin pin for external power supply which has a requirement of min 5V as 3.3V pin will be used to power HX711 module. 5V is converted to 3.3V by on board regulator. During WiFi transmission current requirement will be 600mA. Regulated power supply will involve another linear regulator circuit is extra circuit design, testing, manufacturing and assembly. Ignoring cost, power and other factors, which unregulated external power source can be used ? 4 AA or AAA in series ? C or D ?

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Interestingly, if you look at the Tasmota project, it has support for the hx711 out of the box.

As to what batteries to use, how long do you want the unit to run for? Li Ion 18650 batteries are an option.