The *CHIP* has an ADC range of 0-3.3V.
The *BOARD* has an ADC range of 0-10V.
The input on the BOARD goes through a roughly 3:1 resistive divider before being presented to the CHIP input.
Weighing Sensor for WebControl
- Thread starter ChubRock1
- Start date
The *CHIP* has an ADC range of 0-3.3V.
The *BOARD* has an ADC range of 0-10V.
The input on the BOARD goes through a roughly 3:1 resistive divider before being presented to the CHIP input.
Analog input is 10V, I think Ross and CAI_support were talking about if the resistors before the ADC removed .
You know the old saying - give them an inch and they will take a foot.... <grin>
Any chance you could extend the number of counters beyond one??
CAI_Support
Senior Member
I am sorry to say that is not possible due to hardware counters are used up in this chip. The requirement for pulse being count by raising edge after falling edge is also limitation of hardware. When start to count, if you did not pay attention to that, you will miss a count. However, when measure frequency, the incoming pulses are continuous, so that is not a problem.
Unfortunately, 32bit chip don't have more hardware counters than this 8bit cousin. Its counter implementation is not based on this, so it can not count to 2MHz frequency pulses.
@fwd03- I am still waiting on my INA125 chips but I will certainly post with updates after. (or likely pleas for help).
I did decide to skip the fcounter approach as I am already using LarsK's Polling Tool to capture and track temp and humidity into an excel file which auto updates a webpage so we can keep track realtime. (I attached a screenshot) So it is very simple for me to just add the three analog inputs to the Polling Tool and capture them in the excel sheet and do the conversions from Volts to Weight in excel then have that post to the webpage as well.
[sharedmedia=gallery:images:505]
I did decide to skip the fcounter approach as I am already using LarsK's Polling Tool to capture and track temp and humidity into an excel file which auto updates a webpage so we can keep track realtime. (I attached a screenshot) So it is very simple for me to just add the three analog inputs to the Polling Tool and capture them in the excel sheet and do the conversions from Volts to Weight in excel then have that post to the webpage as well.
[sharedmedia=gallery:images:505]
apostolakisl
Senior Member
The weight sensor is getting very complex it would seem.
Ideally, what would work would be a strain gauge that operated on 5v input and output 0-5v. This would require nothing additional, just 3 wires to make the connection to cai. You could hang a basket off of the strain gauge and you are done.
To the best of my knowledge, no such device exists.
The closest I have seen are the Freescale pressure transducers. I have used a number of these devices with my CAI and they work quite well. While slightly less than elegant, an air bladder with a small tube connected to the pressure transducer port would become a scale.
A relatively simple construct for this would be a glass syringe with a vinyl tube connected to a freescale transducer. The glass syringe plunger would support your weighing platform. Fill the syringe with a couple cc's of air and put a platform on it for supporting your medium that needs weighing. Calibrate your reading as 0. Add known weights and calculate a pressure-weight curve.
Something like this:
http://www.ebay.com/itm/All-glass-Syringes-Syringe-lot-USA-and-Japan-Syringes-Tomac-Ideal-are-usa-/251162380658?pt=LH_DefaultDomain_0&hash=item3a7a71c972
Glass syringes have almost no resistance on the plunger movement which is why you use them versus rubber plunger/plastic syringes.
Ideally, what would work would be a strain gauge that operated on 5v input and output 0-5v. This would require nothing additional, just 3 wires to make the connection to cai. You could hang a basket off of the strain gauge and you are done.
To the best of my knowledge, no such device exists.
The closest I have seen are the Freescale pressure transducers. I have used a number of these devices with my CAI and they work quite well. While slightly less than elegant, an air bladder with a small tube connected to the pressure transducer port would become a scale.
A relatively simple construct for this would be a glass syringe with a vinyl tube connected to a freescale transducer. The glass syringe plunger would support your weighing platform. Fill the syringe with a couple cc's of air and put a platform on it for supporting your medium that needs weighing. Calibrate your reading as 0. Add known weights and calculate a pressure-weight curve.
Something like this:
http://www.ebay.com/itm/All-glass-Syringes-Syringe-lot-USA-and-Japan-Syringes-Tomac-Ideal-are-usa-/251162380658?pt=LH_DefaultDomain_0&hash=item3a7a71c972
Glass syringes have almost no resistance on the plunger movement which is why you use them versus rubber plunger/plastic syringes.
CAI_Support
Senior Member
Hi Lou, strain gauge will be simpler. However, load cell provides much higher accuracy, normally about 1g of the full scale. Even considering all the factors, the result will be like better or about 1% accuracy.
apostolakisl
Senior Member
Are there any load cells out there that return analog voltage or pulse freq that fit directly into webcontrol board ranges?
That's why I like the pressure transducer (which I am pretty sure is a load cell designed for air load). It returns voltage from .2 to 4.8v when you provide it 5v. It is also cheap ($12). The transducer I have been working with on a project measures from 0 to 1.5 psi and is very sensitive. So it would probably be too sensitive for measuring a steak that probably weighs a few pounds. Maybe the 0 to 15 psi model. If you used a syringe with a 1/2 square inch cross section, your load range would be 0 to 7.5 pounds.
CAI_Support
Senior Member
load cell is a popular element in the coomercial scales. Its output normally in 1-10mV range with 10V supply. They all have some kind of amplifier to make the output to the A/D range. There are load cell can weight up to 100 tons, or as low as 100g. Load cell normally can tolerate overweight twice its rated max weight.
If the pressure transducer has load cell inside, it must have amplifier inside, too. INA125 is not that expensive if purchase from suppliers like :
http://www.mouser.co...eoejOqPmWJgMBQ=
or
http://www.digikey.com/product-detail/en/INA125PAG4/INA125PAG4-ND/1509732
If the pressure transducer has load cell inside, it must have amplifier inside, too. INA125 is not that expensive if purchase from suppliers like :
http://www.mouser.co...eoejOqPmWJgMBQ=
or
http://www.digikey.com/product-detail/en/INA125PAG4/INA125PAG4-ND/1509732
apostolakisl
Senior Member
Do you have links to load cells on digikey or similar? This is where I started my original search some time ago when I was also trying to make a CAI scale. I could find nothing that didn't cost hundreds of dollars.
The amplifier is definitely not a cost issue. Of course there is the PITA of wiring it all up on a circuit board.
This is what I have been using. http://www.freescale.com/files/sensors/doc/data_sheet/MPX5010.pdf They cost about $15 as a one off purchase from digikey. They only refer to its pressure sensing part as a "sensing element". And, yes, they list 2 built-in components that are used for amplification and calibration.
Just wanted to remind people that the original poster is using this in a smoker. It changes temperature. Anything using a volume of AIR is going to be hideously inaccurate as a weighing platform.
A loadcell or strain-gauge or other device that isn't going to be so sensitive to temperature changes will be a far better option for this application.
LarsK
Active Member
apostolakisl
Senior Member
That isn't the case here. The container itself is not statically bounded so expansion of the gas does not increase the pressure. Only the weight of the object increases the pressure. The syringe would push the plunger up as the gas expands so the pressure would stay the same and would only be affected by the weight of the object pushing down on the plunger.
This would be true in a confined space, one in which the volume was not allowed to change.
EDIT:
And come to think of it. Using a system such as I have outlined holds advantages in a smoker. I don't know how hot you are getting your smoker (when I smoke brisket I do it about 200 degrees) but heat would adversely affect most electronics. With the air pressure device you can run the airline outside of the smoker and keep the transducer in a cool space.
EDIT AGAIN: Read the original post. He is curing meat, not smoking it. I believe this is done at temps in the "root cellar" range. Cool in other words.
CAI_Support
Senior Member
I think Lou's idea would work, too. Just the syringe may introduce some fritction. That will be the minimum tolerance of the measurament. Because meat curing is a slow processor, the weight decreases over the time. When last few drops of moisture evaporated, the weight loss may not be registered, if the friction is greater than the weight change. But friction is probably in a few gram range, in most cases, that can be ignored.
