Electronics > Beginners
Load cell question
german77:
I need to measure the weight of some trucks. I got a proper measuring device "rice lake 720i" that allows me to print receipts to a serial printer.
I can read what the serial device sends without a problem. But the employees some times take measurements without printing the receipt and keep the money for themselves.
I could make the serial port to send the weighted value all the time but the printer will not work properly anymore. Then I got a brilliant idea, what if I measure with a hx711 the same loadcell. Then I will know if someone measures something and if it's not registered. I can be calibrated from the rice lake device.
Then I realized that there may be a problem. A load cell works with voltage. The rice lake uses 10v and ground for E+ and E-, that makes A+ and A- to be around 5v. Also the maximum voltage that hx711 handles is 5.5v. But I'm using a raspberry so that makes it 3.3v.
But since I only need to measure the difference between A+ and A- that would be way less than 1V. If I do not connect E+ and E-. I will not be referenced to those 5V. And That would mean that the hx711 will work properly without causing damage to the hx711 or the raspberry.
I am right or there is something I'm missing. Or what can I do to make the hx711 to work.... I could use a buffer op-amp and a voltage divider to change the voltage to a proper level. But from previous experience that would introduce a lot of noise and temperature instability.
Karlo_Moharic:
Put up some schematics , because right now , you are not making a lot of sense
german77:
I feel that there is no need for schematics, as everything is a standard. But I will put them any way.
tooki:
Seems to me that all you need to do is to enact the same policy that other stores use which have had problems with employees pocketing the money: Post a sign for customers to see, saying "If we don't give you your receipt, it's free." This gives the customer a really good incentive to police your employees — if they don't get a receipt, then they want their money back!
german77:
The receipts are only for internal administration. The ones handed to the buyers are handwritten |O also the employees are also the ones who stole the product. You will be amazed the many way's they manage to disappear 1 ton of the product. Firing them will not solve anything as 80% of the employees are not even mine. From the internal administration, loss of product it's not that big of a problem. The real problem it's when other companies say that they are missing product.
The setup I'm creating is take photos and info of the trucks, before and after they are loaded. That way I will have more control of my employees to manage them to register every truck. And with other companies to show evidence that the truck left with that amount of product.
I just found out. That my model has two serial ports. And they can be configured differently, that's great because I can use one for printing and another for the raspberry. But the 720i is not the only model they use. That would mean that not every model will have a second serial port.
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