Is a schematic available? Can the board components tolerate a 10v supply so the range goes to 1750 deg C? If not what should be changed?
The 8495 is ok to 36v supply.
AD8495 breakout thermocouple amp P/N 1778
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Please be positive and constructive with your questions and comments.
- adafruit_support_rick
- Posts: 35092
- Joined: Tue Mar 15, 2011 11:42 am
Re: AD8495 breakout thermocouple amp P/N 1778
The product page lists the voltage range for the board as 3-18V, so you should be OK
- C_schroeder
- Posts: 1
- Joined: Tue Jun 10, 2014 5:46 pm
Re: AD8495 breakout thermocouple amp P/N 1778
The eagle schematics and brd files would be super useful as I would like to integrate it into a larger design.
- adafruit2
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-
- Posts: 4
- Joined: Wed Jul 16, 2014 5:27 pm
Re: AD8495 breakout thermocouple amp P/N 1778
Is a data sheet for this breakout available? I am confused regarding the voltage I am getting out of the breakout board....it does not match the table from the application notes for the AD8495 http://www.analog.com/static/imported-f ... N-1087.PDF
According to the application notes, with a junction temperature of 60 degrees, the AD8495 should output 301mV....based off the equation posted on your site, 60 degrees equates to 1.55V ?
The voltage I measure coming out of the breakout board seems to be amplified by a factor of 10?
btw, I think the equation posted on site is incorrect in that ((1.5-1.25) / .005) = 50...not 60.
Please help!
PS I am powering with 5V from arduino Mega.
According to the application notes, with a junction temperature of 60 degrees, the AD8495 should output 301mV....based off the equation posted on your site, 60 degrees equates to 1.55V ?
The voltage I measure coming out of the breakout board seems to be amplified by a factor of 10?
btw, I think the equation posted on site is incorrect in that ((1.5-1.25) / .005) = 50...not 60.
Please help!
PS I am powering with 5V from arduino Mega.
- adafruit_support_rick
- Posts: 35092
- Joined: Tue Mar 15, 2011 11:42 am
Re: AD8495 breakout thermocouple amp P/N 1778
That's because of the Vref factor of 1.25, which is subtracted from the 1.55 to get 0.300.Creo wrote:According to the application notes, with a junction temperature of 60 degrees, the AD8495 should output 301mV....based off the equation posted on your site, 60 degrees equates to 1.55V ?
We add the Vref to the signal so that the module can measure negative temperatures.
Good catch - I'll notify the website peopleCreo wrote:btw, I think the equation posted on site is incorrect in that ((1.5-1.25) / .005) = 50...not 60.
- adafruit2
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Re: AD8495 breakout thermocouple amp P/N 1778
MATH! fixed!
-
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Re: AD8495 breakout thermocouple amp P/N 1778
Ah...the missing piece haha. Now the output I am getting makes sense and I think I figured out how to modify Marlin so I can use with my printer.adafruit_support_rick wrote: We add the Vref to the signal so that the module can measure negative temperatures.
Thanks!
-
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Re: AD8495 breakout thermocouple amp P/N 1778
This post is just FYI for anyone that may need.....
The equation, Temperature = (Vout - 1.25) / 0.005 isn't directly useable with analogread() and Arduino Mega....unless I am missing something. You will have to first convert the ADC value back to the voltage seen by controller pin.
This does work though...int rawADC = analogRead(3); //stores ADC output of read voltage
float Vin = ( 5.0 * rawADC ) / 1024.0; // converts and stores ADC value to voltage seen by Atmel pin
float Vout = Vin - 1.25; //remove added Vref to get actual temp voltage from AD8495
float celsius = Vout / .005; //converts to temperature in celsius
temp conversion equation in one step.... float celsius = (((5.0 * rawADC) / 1024) - 1.25) /.005;
This equation will not work in Marlin though due to oversampling. Here is equation I used in Marlin to get it to work:
return (((((raw * 5.0) / 1024.0) / .005) / OVERSAMPLENR) * TEMP_SENSOR_AD8495_GAIN) + TEMP_SENSOR_AD8495_OFFSET;
Also set TEMP_SENSOR_AD8495_OFFSET to -250. 250 is equal to the 1.25 volts being added by breakout.
The equation, Temperature = (Vout - 1.25) / 0.005 isn't directly useable with analogread() and Arduino Mega....unless I am missing something. You will have to first convert the ADC value back to the voltage seen by controller pin.
This does work though...int rawADC = analogRead(3); //stores ADC output of read voltage
float Vin = ( 5.0 * rawADC ) / 1024.0; // converts and stores ADC value to voltage seen by Atmel pin
float Vout = Vin - 1.25; //remove added Vref to get actual temp voltage from AD8495
float celsius = Vout / .005; //converts to temperature in celsius
temp conversion equation in one step.... float celsius = (((5.0 * rawADC) / 1024) - 1.25) /.005;
This equation will not work in Marlin though due to oversampling. Here is equation I used in Marlin to get it to work:
return (((((raw * 5.0) / 1024.0) / .005) / OVERSAMPLENR) * TEMP_SENSOR_AD8495_GAIN) + TEMP_SENSOR_AD8495_OFFSET;
Also set TEMP_SENSOR_AD8495_OFFSET to -250. 250 is equal to the 1.25 volts being added by breakout.
- marteke
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- Joined: Wed Jul 09, 2014 10:00 am
Re: AD8495 breakout thermocouple amp P/N 1778
how can I stop the oscillation of ad8495?
which equation to use 3.3V?
thank you
- adafruit_support_rick
- Posts: 35092
- Joined: Tue Mar 15, 2011 11:42 am
Re: AD8495 breakout thermocouple amp P/N 1778
As you can see from the A4 raw readings, you're at the limit of precision of the ADC. Try using a 3.3V external reference - the 3.3V reference is a little more stable.
Connect a jumper from 3.3V to AREF. Add this line to setup()
Change the voltage conversion to multiply by 3.3V:
Connect a jumper from 3.3V to AREF. Add this line to setup()
Code: Select all
analogReference(EXTERNAL);
Code: Select all
double Vin=(3.3 * A4);
- marteke
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- Joined: Wed Jul 09, 2014 10:00 am
Re: AD8495 breakout thermocouple amp P/N 1778
I talk about AD8495, just to know!
thanks for the tip, but it´s the same!
now a have other problem, a big one!
here water boils at 98C, my sensor measures 104C, but in ice it measures -4C. as you see is not linear error! in 160C up 180C the error is about 10C plus.
I'm using a power supply 6V with good stability. abouve, there is a part of code.
//-------------mostra termometro esquerdo-------------
if (inicio==0 || vai==0 || ok==0){
if (millis() - lastTick >= 1000) {
lastTick = millis();
float Vin=(5.0*analogRead(4))/1023.0; //___Read AD8495 in A4
float Vout=Vin-1.25;
t = Vout/.0045;
tft.fillRect(15,15,114,46,WHITE);
tft.textTransparent(RA8875_BLACK);
tft.textSetCursor(20,30); //PRINTE TEMPERATUTA
tft.print(t); //PRINT TEMPERATURAsor
Serial.print(Vin);
Serial.print(Vout);
Serial.println(t);
}
}
//-------------mostra termometro direito -------------
if (iniciod==0 || vaid==0 || okd==0){
if (millis() - lastTickd >= 1000) {
lastTickd = millis();
float Vin=(5.0*analogRead(0))/1023.0; // Read AD8495 in A0
float Vout=Vin-1.25;
td = Vout/.0045;
tft.fillRect(355,15,114,48,WHITE); // CAIXA TEMPERATURA REAL 2
tft.textTransparent(RA8875_BLACK);
tft.textSetCursor(359,30); //PRINTE TEMPERATUT
tft.print(td); //PRINT TEMPERATURAsor
}
}
if you have any suggestions, I would like to know.
thanks
thanks for the tip, but it´s the same!
now a have other problem, a big one!
here water boils at 98C, my sensor measures 104C, but in ice it measures -4C. as you see is not linear error! in 160C up 180C the error is about 10C plus.
I'm using a power supply 6V with good stability. abouve, there is a part of code.
//-------------mostra termometro esquerdo-------------
if (inicio==0 || vai==0 || ok==0){
if (millis() - lastTick >= 1000) {
lastTick = millis();
float Vin=(5.0*analogRead(4))/1023.0; //___Read AD8495 in A4
float Vout=Vin-1.25;
t = Vout/.0045;
tft.fillRect(15,15,114,46,WHITE);
tft.textTransparent(RA8875_BLACK);
tft.textSetCursor(20,30); //PRINTE TEMPERATUTA
tft.print(t); //PRINT TEMPERATURAsor
Serial.print(Vin);
Serial.print(Vout);
Serial.println(t);
}
}
//-------------mostra termometro direito -------------
if (iniciod==0 || vaid==0 || okd==0){
if (millis() - lastTickd >= 1000) {
lastTickd = millis();
float Vin=(5.0*analogRead(0))/1023.0; // Read AD8495 in A0
float Vout=Vin-1.25;
td = Vout/.0045;
tft.fillRect(355,15,114,48,WHITE); // CAIXA TEMPERATURA REAL 2
tft.textTransparent(RA8875_BLACK);
tft.textSetCursor(359,30); //PRINTE TEMPERATUT
tft.print(td); //PRINT TEMPERATURAsor
}
}
if you have any suggestions, I would like to know.
thanks
- adafruit_support_bill
- Posts: 88096
- Joined: Sat Feb 07, 2009 10:11 am
Re: AD8495 breakout thermocouple amp P/N 1778
You can't determine linearity with only 2 measurement points.here water boils at 98C, my sensor measures 104C, but in ice it measures -4C. as you see is not linear error!
Plotted out, that actually looks quite linear. The problem here is the slope. But that is the objective of a 2-point calibration. You need to adjust the slope and offset in your conversion.in 160C up 180C the error is about 10C plus.
- marteke
- Posts: 10
- Joined: Wed Jul 09, 2014 10:00 am
Re: AD8495 breakout thermocouple amp P/N 1778
ok thanks, I wll try it
- gabella
- Posts: 1
- Joined: Mon May 05, 2014 11:25 am
Re: AD8495 breakout thermocouple amp P/N 1778
Depending on my power source to the K-type breakout board, it can show large oscillations. Below is the best I can get. Click to see both histograms.
I have now tried four power supplies to power the breakout board, batteries, a 24Vdc switching P/S with a 5V voltage regulator, and two other switching supplies (bricks) one 32Vdc and the other 24Vdc. The power bricks show especially poor noise performance.
I do see 40kHz (approximately) noise on my power system and I have tried filtering that out, but in the end, having clean grounds, a filtered AC power strip, and using rechargeable batteries on the K-type breakout board gives me the above good behavior. Note the histograms on the left.
Below is about where I started, this is before the batteries but after adding the AC filter and the good grounds. Click on it to see the whole thing and pay attention to the lower histogram...I see for a nominal 22.55 deg C the min can be 16 and the max 27 deg C. The other temperature is on a heated block. Click to see the lower histogram.
Any advice is appreciated, know that I sprinkled large and small ferrites around the system, some RC filtering on the power system, and foil and ferrites on the stepper motor power lines that seem the most egregious source of noise (though now they are unferrited and unshielded and I do as well as the top pix; that fix did not make the top any better).
I just came across the Eagle drawing URL in this forum. Thanks. I will look for caps across the chip power and other such "good practices." Still I cannot be alone in seeing this? Maybe I expect too much. We have a fancy National Instruments module that is full of electronics and it sees a "noise" of less than +/- 0.05 deg C (C-module NI-9211).
FYI, I am working with an 16 bit ADC system with +/- 2V, so a resolution of about 0.06 mV which I actually see when I connect a battery to my ADC.
The top figure is workable for my thermal control needs, but I would like not to have batteries inside my instrument.
Thanks, bill e.g.
I have now tried four power supplies to power the breakout board, batteries, a 24Vdc switching P/S with a 5V voltage regulator, and two other switching supplies (bricks) one 32Vdc and the other 24Vdc. The power bricks show especially poor noise performance.
I do see 40kHz (approximately) noise on my power system and I have tried filtering that out, but in the end, having clean grounds, a filtered AC power strip, and using rechargeable batteries on the K-type breakout board gives me the above good behavior. Note the histograms on the left.
Below is about where I started, this is before the batteries but after adding the AC filter and the good grounds. Click on it to see the whole thing and pay attention to the lower histogram...I see for a nominal 22.55 deg C the min can be 16 and the max 27 deg C. The other temperature is on a heated block. Click to see the lower histogram.
Any advice is appreciated, know that I sprinkled large and small ferrites around the system, some RC filtering on the power system, and foil and ferrites on the stepper motor power lines that seem the most egregious source of noise (though now they are unferrited and unshielded and I do as well as the top pix; that fix did not make the top any better).
I just came across the Eagle drawing URL in this forum. Thanks. I will look for caps across the chip power and other such "good practices." Still I cannot be alone in seeing this? Maybe I expect too much. We have a fancy National Instruments module that is full of electronics and it sees a "noise" of less than +/- 0.05 deg C (C-module NI-9211).
FYI, I am working with an 16 bit ADC system with +/- 2V, so a resolution of about 0.06 mV which I actually see when I connect a battery to my ADC.
The top figure is workable for my thermal control needs, but I would like not to have batteries inside my instrument.
Thanks, bill e.g.
Please be positive and constructive with your questions and comments.