How to Convert Your HX-711 Board From 10Hz to 80Hz

The HX-711 loadcell amplifier board is a robust cheap and an all around "ok" board. for simple tasks of weighing stuff it works out of the box but when you want to do high sample rate operations like sim racing pedals, it lags alittle.

Background:

I am a Mechanical Engineer and I am completely oblivious when it comes to electronics and programming. Most of the time this area is down right scary. So while I was building my Sim Racing Pedals, I had the option of using; potentiometers, Loadcells or Hydraulic Pressure gauges, which unfortunate for me, are all electronics related... I have in the end decided to go with Loadcells. After digging deeper, I learned, I needed something called a Loadcell amplifier. While the mental image I had was an audio amplifier, it turn out to be a dinkly little board that will give me a lot of headaches.

If you decide you can not do de-soldering or soldering, note that all we are going to do is disconnect pin 15 from pin 14 and connect it to pin 16. There are some boards that are made in such a way that you do not need to desolder the chip. (purple board)

You will need a healthy supply of tools for this;

SMD soldering desoldering station

Flux

Solder

Voltmeter

3rd hand

Knife (I used a standard kitchen knife)

Soldering skills. (I never desoldered and soldered SMDs before. this was my first it is not as hard as it seems but I had good equipment. If you do not have a smd soldering station you need to check youtube help videos, there are alot, and see how to do it without one)

The wonderful guys at HoanTV Discord (DIY FFB group) came to my rescue and the hero was no other than rane ( @rane#6025 ). All credit goes to him. I am just the bard, along the ride, telling the story...

while researching I heard that the board needed to be running at 80hz or it would lag for sim racing. I either had to ditch the hx711 which came with all the other rectangular stuff soldered next to it (resistors and capacitors and....) or I had to make my own using a faster chip that I did not have and had no clue how to make anyways...

The choice was clear. It had to be HX711. So rane explained everything "very very very paitiently" and we did a step by step what and how to do list.

First he sent me the HX711 datasheet. I read through it (absolutely made no sense of course) but rane told me that we will be dealing with the pins 15 and 16 (and alittle with 14) So I check what the pins are

Pin 15 is the culprit here. It is called "RATE" and if you connect it to ground, which apperantly means 0, if makes the HX711 work at 10Hz. If you connect it to positive (which is named Vcc just to confuse the living hell out of me) then it becomes 1 (someone shoot me please) and makes the board work at 80Hz. Simple right.....

Now using your voltmeter, check continuity between; (using the buzzer selection.)

Pin 16 and Ground,

Pin 15 and Ground,

Pin 14 and Ground.

On the green board we have here the following occurs;

Pin 16 and Ground, (No sound)

Pin 15 and Ground, (Buzzing)

Pin 14 and Ground. (Buzzing)

So we know that the pin 15 is connected to ground and therefore the board is at 10Hz mode. Unfortunately on this board the trace is under the chip. So you need to remove the chip to do the surgery.

I highly suggest you get to know how to desolder and solder SMDs. Watch some Youtube videos and see if you can handle it. I have seen it done before and I do have an soldering station with a heat gun for SMD operations.

If you do not have a soldering station this is the moment to decide if you should tackle this or not.

The information is valid on how to switch mode technically. Physically if you can do it or not will depend on your skills and equipment.

Now using the desoldering gun I started blowing air from top to the Chip legs from an angle so I did not remove anything else. From the image you can see the shaded area where you should concentrate. I used a small screw driver to lift the Chip as the solder softened and melted. make sure to keep the gun moving and not concentrate hot air to one area. Make sure to use a 3rd hand to hold the board and not wiith your hands...

Once removed you can see the traces and where to cut.

The trace is under the white line so we will cut between 14 and 15.

Now that we know the location, get your trusty sharp knife out (I used a kitchen knife with a sharp edge) and start scraping the trace.

Always pull the blade away from yourself.

Do not rush.

Do not use force. let the blade do the job. you will pass through the white and green paints then you will see the shiny copper trace. keep at it until you see the fiber board. you can see my final result that worked.

No measure the connections between:

Pin 16 and Ground, (No buzzing)

Pin 15 and Ground, (No buzzing)

Pin 14 and Ground. (Buzzing)

Once you hear no buzzing between Pin 15 and Ground, you are done. (well kind of...)

Now you need to resolder the chip back into its original position.

Place the board on a non flamable surface. or hold it with the third hand but make sure it is securely tied to the table.

There is a small dot next to pin 1. Orient it the way you see it in the picture. now gently apply pressure with the knife or a small screw driver to hold the chip in place.

Start blowing air to the legs of the chip until the solder starts to melt and the chip seats into its place.

We are almost done....

Now connect Pin 15 and Pin 16 using a small blob of solder.

Now check Continuity again. This time Pin 15 and pin 16 to ground (no buzzing)

Pin 15 and 16 to Vcc (Buzzing)

Pin 14 to gnd (buzzing)

also check resistance (sigma sign) between Vcc and GND at this point. the result should be Kilo Ohms or higher (I had 6.5Megaohms) and not in ohms. If it is low check smd solders.

Now everything checks go test and enjoy your new High frequency HX711.

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Note:

In your software the serial baud rate needs to be set at 115200 if you are using serial output :

Serial.begin(115200);

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