The Radio Control Temperature Logger (RCTL) Manual For hardware version 1.0 Manual version 1.0b All materials owned by Dan Gebhardt Introduction This device records the temperature of a model engine during a time period (standard is 5 minutes) at a certain interval (standard is 5 seconds) for a total of 60 data points. After this limit, the oldest data is overwritten with the new data, as in a circular buffer. This data is then transmitted to a TI-89 calculator (TI-92, TI- 92+, Voyage 200 should work, but have not been tested as yet) where the temperatures are viewed as a data point plot. From this display, the user can gain valuable information on the operation of the engine. Needed Hardware (supplied by the user) Compatible calculator TI-89 (TI-92, TI-92+, Voyage 200 should work, but have not been tested). Calculator to calculator link cable received with calculator purchase. Computer to calculator link cable this is not included with the calculator purchase, and must be obtained separately. A commercial cable and software package is available from Texas Instruments, or a homemade link cable can be used with free software available designed to use it. Plans can be found on the internet under titles $5 parallel link and $4 serial link. Alternatively, one can be purchased from Dan Gebhardt (see below for contact information). 9-volt battery (or any battery 7.5 volts or higher, with user-modified connector). Soldering iron (and knowing how to use it). Assembly Instructions Add 3.5mm stereo plug to calc-calc link cable. The following steps will give a calculator to calculator link cable with a 3 rd plug (3.5mm) attached near the center to use with the RCTL, homemade link cable,
or other 3 rd party device (2.5mm sockets and plugs are very hard to find, so most non-ti devices use 3.5mm). Step 1 -- Cut the calculator to calculator link cable somewhere in the middle. There should be three conductors: red, white, and bare wire ground (colors may vary). Strip off a portion of outer insulation (main cable) on both halves for about 1 inch. Strip off a portion of insulation on all the colored wires for about ¼ to ½ inch. Twist the conductors together such that they match. Bundle and twist the ground wire strands before twisting together. Solder each of these connections. The steps just completed give a cable that works like the original (connects two calculators together), but allows the addition of another connector by attaching to the bare solder joints. Step 2 Strip 1 inch off of the main insulation coming from the supplied 3.5mm plug. Strip ¼ to ½ inch off each colored wire (white and blue). Twist and solder the white lead to the white joint on the original cable. Do the same for the other wires connect the blue lead to the red joint and the ground wire to the ground wire joint. Wrap electrical insulation tape around each separate connection so that none can touch, then wrap tape around all the connections together. Note that if the original cable wires are of different colors, the user must find out which color goes to the TIP of the 2.5mm plug. This wire will connect to the BLUE lead of the 3.5mm plug. The steps are shown in the photographs below.
Figure 1: standard link cable. Figure 2: cut and stripped link cable. Figure 3: link cable soldered back together with 3.5mm plug addition shown stripped. Figure 4: 3.5mm plug addition soldered onto joints. Figure 5: joints insulated with electrical tape. Figure 6: completed cable with final electrical tape insulation
Mount circuit board and battery in the enclosure. Attach the 9-volt battery to the snap and place in the enclosure. Check for power by moving the slide switch so that the green LED is on. Press the pushbutton and check to see if the red LED comes on during the press. Turn board off. The recommended orientation is with the battery snap facing the right with the connection jack facing toward the user, and for the wires coming out of the snap facing toward the user. Insert the circuit board such that the 3.5mm jack is aligned with the cutout opening in the side of the enclosure. Screw down one side just so the screw bites into the mount. Screw down the other side similarly. Note that the board will need to warp slightly to get the screws to bite the bottom of the circuitry hits the battery, but this is not a problem. The following photo shows this. Figure 7: RCTL ready to be mounted. Attach sensor to board. Plug in the sensor to the vertical two-pin connector. The other end (sensor element) is attached to the engine, but that is done after verifying correct operation.
Calculator Software Setup Load software on calculator. Use your computer to calculator link cable and software to load the supplied calculator programs and data files to the MAIN directory of the calculator. Refer to the documentation of the link cable and software for more information. It should be possible to simply rename the extension of the file to load on the other types of (supposedly) compatible calculators. Below is a description of each program and file: plot.89d the plot file that is displayed in the graph window. rctlog.89p a TI-BASIC program that is the front end to the RCTL calculator software. rctset.89l a list file containing RCTL program settings, namely the calibration slope and intercept values. temprx1.89z an assembly program which receives the raw temperature data from the logger for the flight time (if less than the longest length) and stores it in a list called temps. Temprx2.89Z an assembly program which receives the raw temperature data from the logger (all memory locations) and stores it in a list called temps. temps.89l a list file of the temperatures recorded. times.89l a list file of the times of each data point recording (incremented by the recording interval length). Setup graph data. Make sure the plot variable is the current data file by: push APPS, then number 6 for data editor, then number 2 for open, toggle down to Variable and select plot, press ENTER. Now go into the graph setup menu by pushing the green diamond button then F1. Toggle up to Plot 1 and press ENTER. Set Plot Type is set to xyline, make the Mark whatever you like (dot is recommended). Under x and y type in c1 and c2 respectively. Press ENTER. The graph is now setup. Verify Correct Operation Perform basic communications test. Connect the calculator and RCTL together with the modified calculator to calculator link cable. Turn on the RCTL by sliding the switch, but make sure to not have the pushbutton pressed. Run the rctlog program on the calculator by pushing 2 nd and the - key to go into VAR-LINK. Scroll down until rctlog is highlighted and press ENTER. rctlog( should now be entered in the home
screen. Press the ) key and ENTER. Select the 2 nd menu choice, Rx all, meaning get all data from the RCTL (this is just a test, so the actual values don t matter). Another program will display with the title R/C TEMPERATURE LOGGER which is waiting for data to be sent from the RCTL. Press the button on the RCTL to start the transfer. A bunch of stuff will scroll down on the screen displaying each data value (note, this is not the actual temperature) received. After it finishes, press ESC. Now the main menu should be visible. Select disp graph or number 4 to check the graph setup. This should display some sort of line, or nothing at all (the values are too far down on the Y-axis). Use the arrow keys to scroll through the points. Press ESC when done. Exit the program by selecting EXIT, or pressing number 5. Troubleshooting. If the above step could not be completed, do the following to narrow down the problem: Test communications cable. Do a continuity test from each plug to the other (3.5mm to 2.5mm) and test for proper connections, making sure two of the plug segments are not shorted out (e.g. make sure no continuity between tip and middle, tip and base, etc..). If there is a problem, it can usually be fixed by re-doing the 3.5mm plug extension add-on. Check the voltage of the signal lines coming from the RCTL. This can be done by turning on the RCTL, plugging in the cable to the RCTL (not the calculator), and reading the voltage from the base of the plug to the middle and tip (each should read approx. 5 volts) of the calculator end. If it does not, contact the developer, Dan Gebhardt see below for contact information. Perform recording test. Connect the temperature sensor to the RCTL. Boil a small amount of water in a cup, remove it from heat (stove or microwave) and quickly perform the next steps. Place the sensor in the water taking care the actual element is in the water. The element is the heat-shrink covered section closest to the bend in the wire. It should have an extra layer of heat-shrink over it about ¼ long. Press the button on the RCTL and then slide the switch to turn it on. This starts the recording. The RED LED should stay on. Wait for a length of time, such as 3 minutes, and turn the RCTL off. Connect it to the calculator as before, but use the first menu choice to receive the data this time. The graph should appear similar to the following figure:
Figure 8: Boiling water test data plot Note that the peak temperature measured should be slightly (approx 5 degrees) above the actual boiling point of water at the test altitude. This is due to the complete contact surface the liquid water provides, as opposed to the partial contact surface when mounted on an engine. Flight Test Setup and Operation (the fun part!) Mount sensor. This is the most important operation to assure consistent and accurate temperature measurements. The mounting method used makes use of the premade loops in the signal wire and the magnet wire end, and a cable tie (zip tie) run through them, secured and cinched with the end of another tie. Various locations can be used to mount the sensor. The recommended one is the cylinder fin closest to the head on the side opposite the exhaust port. Other possibilities are: last fin on exhaust side, somewhere on the actual head, or try other places and experiment! Make sure that the element bead itself is being pressed against the metal very firmly! Remember, the element is the doubleheat-shrink part about ¼ long, near the bend in the bare wire (where the enamel coated wire attaches). The following photographs help to illustrate the mounting procedure. NOTE: the photos show the sensor on the exhaust side this was used initially, but after further testing and comparison with other temperature measurement devices, it was found that the side opposite the exhaust gives more comparable results. On the test engine (Thunder Tiger 39 Heli), there was a 40 degree drop in temperature from the exhaust side to the opposite side of the cylinder. Most other devices (such as the Venom) recommend the side opposite the exhaust, as well.
Figure 9: Sensor assembly Figure 10: Sensor assembly mounted (prototype sensor shown, varies on production version).
Figure 11: Sensor fastened around engine Mount electronics. The electronics box can be mounted wherever is convenient. A good place is to rubber-band it on top of the other heli-electronics in the front, although the canopy must be removed to access the RCTL. After this is done, route the sensor wire to the box, and plug it in. Do another communication test to check everything. An example mounting on a Freya is shown in the following photos.
Figure 12: Example mounting on a Freya helicopter Figure 13: Example mounting on a Freya helicopter Use during flight. Get the engine running. Hold down the pushbutton while turning the RCTL on with the slide switch. The red LED should stay lit after releasing the pushbutton.
Put on the canopy. Go fly! After the flight, quickly remove canopy and shut off the RCTL with the slide switch. Get the calculator ready, connect the cables, turn on the RCTL (without pushing the button), run the receive last session option on the calculator program, and push the button to send the data. After this finishes, press ESC, then display graph. Use the arrow keys and trace to view the temperatures on the graph (displayed in the lower right corner as the yc). From experience and other s suggestions, the recommended temperature range for most heli engines is from about 200 to about 230. On a 150 mah 9V battery, it is estimated that run time will be near 7 hours. Other configurations. The setup listed above is the standard RCTL setup, but one might want to consider the following options. To reduce the size slightly, the black plastic enclosure does not have to be used. Instead, the battery can be rubber-banded to the bottom of the board. This is my personal preferred way of mounting. Another option is to mount the RCTL board remotely away from the 9V battery so it can be accessed without removing the canopy. To further reduce the size and weight, the 9V battery can be replaced with any other power source approximately 7V to 13V such as a miniature 12V battery used in garage door openers and other small devices. These batteries are about ½ the size of a AAA. For the daring, one could modify the circuitry to use the receiver battery pack as a power source. This would require replacing the 5V regulator with a 3V or similar regulator, changing the microcontroller code to compensate, and possibly doing a calibration of the sensor. Contact me for other hints. Any future version of this product will be able to run off of the Rx battery pack. Final Words Thank you for choosing to use this new and useful device! It is a product born of my personal desire and curiosity to know at what temperatures my engine is running, and use an already-owned TI-89 as the data display. The development cycle has been very long and difficult, but also very educational. I wish to share what I have learned with others thus all the source code and technical data is available to those who purchase this device. If you would like to know something technical, send me an e-mail. Also if you have any problems or questions with the device, I will try my best to help. My contact information is below. Developer and Seller Dan Gebhardt danatup@softhome.net danatup.netfirms.com/rctl/
Revisions v.1.0b (7/2/03) Changed recommended sensor mount location from exhaust side of cylinder to opposite side based on further experimentation.