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Everything posted by JStat60

  1. JStat60

    Noise in ADC

    That was a good suggestion @spirilis, I posted on the E2E site on the recommendation of the folks at Mouser. Had they not recommended this (and you as well), I would not have done so. The conversation on the E2E site is very helpful. Thanks, Jack
  2. Hi. A while back I had the need to send two bytes of data to a digital potentiometer without changing the state of chip select pin between the two bytes. I ended up modifying the SPI library and calling it altSPI. Essentially, the only change was to add two defined things called trans2ByteA and trans2ByteB. The first of these selects the chip and transmits the first Byte. The second transmits the second byte and then de-selects the chip. These are defined in altSPI.cpp as in the code below. The library can be found at https://github.com/SmokyMountainScientific/altSPI. If I were t
  3. JStat60

    Noise in ADC

    Thanks for the suggestion @PTB but I dont think that is the problem. I am powering these through the USB port on my computer. I am also using the same micro USB cable and there is no change in the quality of data between trials. That is, a good board will always give good readings and a bad one will always give bad readings. Jack
  4. JStat60

    Noise in ADC

    Hi, I have a non-profit (Smoky Mountain Scientific, smokymtsci.com) that develops and sells low cost instruments for science education. One of our instruments incorporates a Tiva-C launchpad that outputs a pwm voltage and measures voltage and current passed in electrochemical reactions. I recently purchased a fairly large batch of Tiva launchpads from Mouser and I am having trouble with noise in the analog read channels for about 1/4th of the boards. We have been building and selling these instruments for a couple of years now and have never had this problem before. To test the boards, I
  5. Does this mean that the solution to this problem has been posted? If so, where? I am trying to link together four tiva launchpads (TM4C123...) and have them communicate using Serial2, Serial3 and Serial4. I want to use an array of serials to simplify the code but I cant get the modules selected. When I try serial[j].selectModule(module[j]); I get the error message "class HardwareSerial has no member named selectModule". Any ideas? Thanks, Jack
  6. Hi Folks, I recently designed a Booster Pack that I intended to use as a recording pH meter. The idea was that it would have a couple of British telecom analog (BTA) connectors that you could use to plug in a pH probe from Vernier instruments. The problem is that I assumed that the pH probe was comprised of a pair of passive electrodes, when in fact it has an amplifier built in and requires power and ground connections in addition to an output. This means that it cant be used as a pH meter (at least not with the Vernier probe), but you can use it for data logging. Of course there are limi
  7. We have been working to develop a low cost, three-electrode potentiostat for use in science education and environmental monitoring. This is a computer driven instrument that is appropriate for teaching at the university (undergraduate) or perhaps high school or home school level. It can be used to teach physical chemistry concepts and can be used to quantify things like metals in water. At this page, we describe using the instrument to measure lead in water at concentrations as low as 44 ppb. The instrument (called the WheeStat) is comprised of a Stellaris / Tiva LaunchPad, a booster pack
  8. Hi Folks, Hope you don't mind answering some possibly dumb questions from someone with very limited coding experience. I recently figured out that I could not communicate with my Stellaris / Tiva launchpads the "device" USB connection. It appears to me that this is the issue that you are working on. Is that correct? If you are able to accomplish what you are attempting, will it be possible to communicate with the launchpads without downloading and installing the ICDI drivers? I would like to use some launchpad based instruments to teach chemistry labs and I foresee installing the drivers
  9. Hi, I appreciate the help. It has taken me a while to get back to this and I am still having issues. I have tried workaround #1 above and got the following error message: "SYSCTL_PERIPH_TIMER2 not declared in this scope". It will accept ROM_SysCtlPeripheralEnable(TIMER2) without generating the error, but that does not get the program working. I am trying to control a digital pot using SPI module0 and I am watching the SPI clock with an osciloscope. When I comment out the analogWrite(PB_0, 100); command I can see the SPI signals on my scope but the program hangs up when I try to run the an
  10. @@energia, I have been using the Stellaris LauchPads (EK-LM4F120XL Rev and a PC running Windows 7. I do have some of the Tiva boards but I did not try this out with them. I have had this problem with multiple programs. In addition to the modified blink sketch reproduced in my 13 Feb post, I was unable to run a rather involved program that can be found at https://github.com/SmokyMountainScientific/WheeStat5_0/tree/master/WheeStat5_0. A third test program (presented below) Incorporates a pwm output into the setup of AnalogReadSerialOut. When the pwm output is on one of the "non-functionin
  11. Thanks for the replies. This appears to be a problem with the newest version of Energia (0101E0011). I recently loaded the newer version and had not gone through and tested it with older code that I knew worked with the previous version (0101E0010). Yesterday I tried loading a program using the new version and the program failed to run. After a prolonged bout of mild cursing, I discovered that the problem was with a PWMWrite command on pin PB_6. Thus, it appears that port B has problems with the new software that did not occur previously (ie, not a hardware issue). I re-installed 0101E0
  12. Thanks for the response. While the original code invoked serial communications, the modified blink program did not. I would consider the possibility that the history of the board could affect its response, except that I was unable to get an analog output from the brand new board. Still it is good to know that serial communications affect what you can and cannot do with various pins. This is still all pretty new to me and that is not something that I would have guessed. Thanks again, Jack
  13. Hi, I use Energia with a Stellaris LaunchPad and I can write pwm signals to some pins but not to others. I have no trouble writing to the red, green or blue leds, or to PB_5. I cannot seem to get a pwm signal out of PB_0 or PB_1. I thought that I might have damaged my LaunchPad so I tried with another board and got the same result. Guessing that I could have two damaged boards, I got a new one out of the box and it behaved in the same way. All the pins in question should be able to output pwm signals (according to the energia reference page). The code I am using to test the output is jus
  14. Problem solved. This was a hardware issue. I guess I cooked the digital pot while trying to solder it to the board. Replacing the pot resulted in behavior predicted for my test circuit. In case anyone is interested, I have pasted the energia code I tested the pot with below. The circuit is described as well. The sketch uses the trans2byte commands described above and the SPI library from Reaper7 and Rei Vilo. Sorry for the confusion. Jack /* Sketch for testing MCP 4231 digital potentiostat with volatile memory. modified from the Digital Pot Control example that comes with Ene
  15. Hi, I am new to coding and I am having trouble setting wipers on a digital pot. The pot I am using (MCP4231) requires a 16 bit instruction to set the wiper position. The reference sheet indicates that chip select stays low for 16 clock cycles. Using the library posted by Reaper7 and Rei Vilo (big thanks, by the way), I was able to transfer 2 x 8 bit bytes, but that did not reset the wipers. (I have access to an oscilloscope, so I can see what is going on). Figuring that the problem was that the chip select goes high between the two transfers, I put the following into my SPI library:
  16. Hi, I am kind of new to microcontrollers and really never did any coding prior to about three years ago. I started with arduino and quickly changed over to the MSP 420 launchpad. I began the transition to the Stellaris a couple of weeks ago and I am having trouble with the spi(0). I am a university chemistry professor and my interest in microcontrollers stems from my desire to develop low cost, open-source instrumentation for teaching chemistry at the high school / commmunity college / university level. Well, that is me. Jack
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