Trying to detect if Ping sensor is connected
Don M
Posts: 1,652
in Propeller 1
I'm looking at the Ping object and see that it returns a value when called. How do I abort the call when there isn't a Ping connected? Or maybe a better question is what is returned if there is no Ping connected? Does it just hang because it never sees the pin go high or low? If so how do I get past it? Maybe a watchdog timer?
Thanks for any help.
BTW- first post in the new forum format...
Don
Thanks for any help.
BTW- first post in the new forum format...
Don
Comments
The easiest thing to do is to comment out the Ping code rather than add more code for a watch dog timer or some sort of test of presence.
In fact, I have strong doubts that you can write code to see that the Ping is not attached. You might start having to track what is physically plugged in by building a special interlock.
As best as I can recall, the Ping only returns a pulse when it hears one and that can be a long, long time if it isn't moving and nothing moves in front of it.
I think the Ping object in the Propeller library will hang if no Ping connected. A watchdog timer is probably the easiest way to check if a Ping is connected. At least it's the easiest way I can think of.
Edit: If you have a spare I/O pin, I think there's a way to modify the Ping object so one I/O pin will change after a timeout period (using a counter). Instead of having the waitpxx wait for a change on a single pin, it could look for a change on two pins so the timeout pin will free the cog from continuing to wait.
There wasn't a timeout here but this shows what the line is doing while a measurement is taking place.
The Ping code toggles the signal line (the short pulse seen in the trace) and sets it as an input. The code both waits for the pin to go high and then waits for the pin to go low. If no Ping is connected, this will cause the cog to freeze.
Since the code leaves the signal line pin low and an input, it could be forced to terminate by another cog without the need of a second I/O pin. The other cog could set the pin as an output and toggle the line to stop the cog from waiting for the pin state changes.
Here is the code from this object and what I don't understand is where the variable "Echo_Length" gets it's value from. In the beginning of the repeat loop it is assigned to the variable "Distance" in this statement- Distance := Echo_Length >> 1
CON _clkmode = xtal1 + pll16x 'Standard clock mode * crystal frequency = 80 MHz _xinfreq = 5_000_000 Ping_Pin = 11 ' Pin that Ping))) Sensor is wired to DPu = 13512 {{ DPu assumes Speed of Sound to be 1126 Feet per Second in Dry Air @ 68 °F. 1126 * 12 = 1352 inches per second }} VAR long Sensor_Pin long Echo_Length long Distance long uSec long Raw_Distance long Remainder OBJ pst : "Parallax Serial Terminal" PUB start : okay pst.start(115_200) ' Start the Display Sensor_Pin := Ping_Pin ' Prepare Variable cognew (@entry,@Sensor_Pin) ' Start Assembly Routine in a new COG waitcnt(clkfreq + cnt) ' Wait a second ' Prepare Display screen with Labels for data to be shown pst.str(string(" PING))) Demo",13,13)) pst.str(string(" Raw Count in CLOCK Cycles........",13,13)) pst.str(string(" One Way Time in CLOCK Cycles.....",13,13)) pst.str(string(" µSeconds to Target...............",13,13)) pst.str(string(" Distance in Inches...............",13,13)) repeat pst.Position(34,2) pst.ClearEnd pst.dec(Echo_Length) 'Raw Count in CLOCK Cycles Distance := Echo_Length >> 1 pst.Position(34,4) pst.ClearEnd pst.dec(Distance) 'One Way Time in CLOCK Cycles uSec := Distance / 80 pst.Position(34,6) pst.ClearEnd pst.dec(uSec) 'µSeconds to Target pst.Position(34,8) pst.ClearEnd Raw_Distance := uSec * DPu / 1_000_000 Remainder := uSec * DPu // 1_000_000 pst.dec(Raw_Distance) 'Distance in Inches pst.char(46) 'Print decimal point pst.dec(Remainder) 'Distance fractional portion waitcnt(clkfreq/4 + cnt) 'Wait to do it again Dat entry org 0 rdlong P_Pin, par 'Read Main Ram to find out Pin Ping)) is wired to. mov Pin, #1 'Set a 1 into "Pin" shl Pin, P_Pin 'Shift the 1 to Pin bit add Trigger_Counter, P_Pin 'Add Pin into APIN of Counter add Echo_Counter, P_Pin 'Add Pin into APIB of Counter mov Echo_to_Main_Ram, par 'Echo_to_Main_Ram is distance to be returned. add Echo_to_Main_Ram, #4 'Make it the second Variable in the list mov frqa, #1 'Set frqa to count 1 per clock mov time, cnt 'Get original time stamp :loop add time, Echo_Holdoff 'Add Echo_Holdoff to time mov ctra, Trigger_Counter 'Set counter to NCO single-ended mode or dira, pin 'Set APIN to be an output neg phsa, Trigger_Pulse 'Send Trigger Pulse 2 µsec pulse waitcnt time, Echo_Pulse 'Wait for Echo_Holdoff 750 µsec muxc dira, pin 'Make Ping))) Pin into an Input mov ctra, Echo_Counter 'Time Echo Return Pulse mov phsa, #0 'Clear the accumulator waitcnt time, Delay_B4_Next 'Wait for pulse to complete ≈ 21.7 msec max mov Echo, phsa 'Read Echo Return Pulse length wrlong Echo, Echo_to_Main_Ram 'Write the result to Main Ram waitcnt time, #0 'Wait B4 taking another measurment jmp #:loop 'Loop forever Trigger_Counter long %00100_000_00000000_000000_000_<< 6 'NCO single-ended Mode Echo_Counter long %11010_000_00000000_000000_000_<< 6 'LOGIC A Mode Trigger_Pulse long 160 '2 µsec Trigger Pulse Width Echo_Holdoff long 60_000 '750 µsec wait B4 Measuring Echo Pulse Echo_Pulse long 1_924_000 '1_924_000 for 40 reads per second Delay_B4_Next long 16_000 '200 µsec Delay B4 Next Cycle Pin res 1 P_Pin res 1 time res 1 Echo res 1 Echo_to_Main_Ram res 1 fitto this and it works when the Ping is disconnected but what I'm wondering is where the Echo_Length variable gets its value from in the first place.
if Echo_Length == 0 pst.str(string("Not connected")) else pst.dec(Echo_Length) 'Raw Count in CLOCK CyclesIt would be important to not change the order of the variables in VAR without changing line 8 in the pasm.
Tom