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 Tell me about GPS Speed Signal waveform...Jump to page : 1 Now viewing page 1 [50 messages per page] | View previous thread :: View next thread |
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buschman |
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Farming in Michigan | Would like to switch from wheel drive to GPS speed signal on our planter, interfacing to Early Riser 3 monitor with the 4-pin connector for speed input. Would also like to have a speed display in some of our older equipment. I can pick up a Sensor-1 or similar GPS Puck but would rather tinker with some of the newer Arduino GPS offerings. Would like to put together a GPS module, LCD speed display, and output the speed signal to the planter monitor. I see lots of examples out there, the unique thing here is interfacing to the monitor. The arduino would read the GPS signals and parse out the speed data. The question is what pulsetrain do i need to feed my monitor? I recognize I probably need to use all 4 pins to trigger the monitor into looking for a "fast" signal vs that from the wheel speed sensor. I believe the Sensor-1/gps pucks spit out a ~57Hz signal, do these units vary the signal amplitude as the speed changes? Just looking to put together a fun project and let the kids learn a little about GPS & electronics in a practical application. Thanks. | ||
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| Rod Maker |
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Westport, IN | I'm working on an Arduino Project now. The signal out would be very easy. Rate per mile per hour isn't important just so they match each other. What I'm not sure of, as this my first project, can the Arduino run in parallel the output flashes, while reading the GPS signal is being received. Maybe the GPS runs outside of the Arduino main loop?? Good luck, and keep us posted. | ||
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| AllSand |
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Eastern SD | Believe it or not there isn't an absolute standard for a radar or simulated radar signal. Thus most devices have a way to calibrate the speed signal they receive. All that I have encountered use a change in frequenxy, not a change in amplitude. Some documentation shows the rate as Hz per MPH. That seems like a strained unit to me. One 'standard' is 50 pulses per meter. If you get position data at 5 Hz it will be up to you to do any necessary filtering prior to setting the output clock. Probably not necessary, but you could also use algorithms to take into account accelerations. You can update your output faster than the 5Hz you get updated GPS position, so can smooth the change in output speed instead if having big step changes each time you get a new position. | ||
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| tedbear |
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Near Intersection of I-35 & I-90 Southern Mn. | I've messed with Arduino a bit but not for your type projects. Concerning the pins for your Early Riser. I am quite solid on the their purposes. I'm not so positive on the pin numbers. One Pin on the Early Riser plug is to provide a 12V power source for a real radar gun or the hockey puck GPS. Another Pin is Ground. which is ground for the power for the radar or hockey puck and signal ground. Another Pin is the actual signal itself (which is the whole reason for doing this). I'm thinking that Pin 1 is ground, Pin 2 signal, Pin 3 is 12V iIN and Pin 4 is radar detect (12V OUT when attached to a radar gun). The fourth pin is sometimes used and sometimes not even present. With certain Early Riser planter modules, the operator had the choice of using a radar gun or a ground speed sensor. Rather than having a switch so the operator could make the choice it was done automatically. Here's how: inside the Dickey John radar gun the pin receiving the 12V power has a loop back to Pin 4. Pin 4 on the monitor side will then receive 12V if it is connected to a radar gun. If it is connected to a ground speed sensor there is no pin 4 so the monitor would NOT see 12V on Pin 4. This means that upon initial startup, the program inside the Early Riser polls pin 4 to decide whether a radar gun is attached. If so the program uses a routine appropriate for radar speed, otherwise it assumes a ground speed sensor and behaves differently. I ran into this when I would make adapters to use a radar gun already in the tractor to an Early Riser Monitor. I had to provide 12V on the Pin 4 so that the Early Riser would perform properly. My opinion is that the signal produced by a real radar gun or a GPS speed device is the common short to ground routine used by flow meters and most ground speed sensors. I am of the opinion that the system "counts" the pulses in a given unit of time and uses the speed Cal number to convert those pulses to usable units of distance and speed. So I believe that the output from the Arduino would only need to vary the speed or frequency to provide a signal for the Early Riser. I agree on the 57Hz value since some GPS units that can produce emulated radar OUT have a menu choice to set the frequency. By trial & error I have found that setting them at 57Hz produces an output similar to a radar gun thus allowing the device to use its "old" speed cal number. I don't know the mathematical meaning of the 57HZ but it must mean 57HZ is produced at a certain ground speed or distance. When I turn on the emulated radar out with my Ag Leader 6500, the code contains the number 36.11, 5HZ, 500 and 5. I have no idea what these numbers mean but they cause the 6500 to output a radar like signal that I have back fed into the tractor dash. I have used speed simulators for Raven 440s etc that were a fairly simple circuit consisting of the old 555 timer and some external components involving a "pot" for adjusting the pulse output. If I were going to do this with an Arduino, I would first setup up a breadboard and a sketch that just produced an output that went to ground (modified Blink Sketch) to see if I could "see" speed on the device in question (planter monitor, Raven 440 etc). Once this was successful then I would approach getting this information from a GPS shield or other source. | ||
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| raider2b |
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North Dakota | All "radar" inputs are in pulses/mph. The default for a Dickey John radar is 58.94 hertz/MPH for ag use. There are different outputs but most are 59. It is just a 1.5 millisecond pulse of voltage if I remember correct. GPS speed is actually velocity measured in knots or KM/H. For example VTG is true degrees, magnetic degrees, speed in knots and speed in KM/H. Other methods use simple lat/long comparisons and a bit of Trig to calculate speed. Most cheap GPS receivers are only capable of outputting GPS messages at 1/second, some of the cheapest are only capable of one message every 5 seconds. The sensor one speed is output at 5/second. For a planters/drills we have found that the most reliable, fastest updating and accurate speed comes from the wheel speed sensor. | ||
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| hillfarmer |
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raider2b - 5/28/2018 08:54 All "radar" inputs are in pulses/mph. The default for a Dickey John radar is 58.94 hertz/MPH for ag use. There are different outputs but most are 59. It is just a 1.5 millisecond pulse of voltage if I remember correct. GPS speed is actually velocity measured in knots or KM/H. For example VTG is true degrees, magnetic degrees, speed in knots and speed in KM/H. Other methods use simple lat/long comparisons and a bit of Trig to calculate speed. Most cheap GPS receivers are only capable of outputting GPS messages at 1/second, some of the cheapest are only capable of one message every 5 seconds. The sensor one speed is output at 5/second. For a planters/drills we have found that the most reliable, fastest updating and accurate speed comes from the wheel speed sensor. " the most reliable, fastest updating and accurate speed comes from the wheel speed sensor" until the planter harness, gets pinched in the folding process | |||
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| KMech |
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Missouri | I have found planter wheel speed sensors to be adequate, but in the event GPS or radar are available, they are better alternatives. Wheel speed sensors are only as accurate as their calibration, and that calibration is only accurate in those soil conditions. Changes in soil type/firmness/moisture or tillage vs no-till planting can have varying effects on how the wheel rolls and the resultant amount of slippage. GPS is more accurate, but can be a little sluggish in response to speed changes. It seems to take a half a second to register speed when starting from a standstill. I have found radar to be the best in terms of accuracy, repeatability, and response time, although I must include an asterisk with that statement. My observations have been with a John Deere dual beam radar. By nature of the dual beam design, it self-corrects for changes in beam angle, thereby never needs recalibration. I haven't had the opportunity to test single beam radars. | ||
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