Difference between revisions of "Frequency Counter"

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(Created page with "{{i18n|Frequency Counter}} {{Module |NAME=Frequency Counter |MENUCONFIG={{Applications}}->Frequency Counter |STATUS={{stable}} |PINNING=yes |ECMD={{has_ecmd}} |DEPENDS=ECMD (…")
 
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Measures the frequency and duty cycle of a signal
 
Measures the frequency and duty cycle of a signal
  
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== Anschluss ==
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== Pinning ==
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* muss immer an das ICP1-Pin angeschlossen werden
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* the signal must always be fed to the ICP1-pin. Look up in the datasheet which physical pin this is on the used controller.
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* im Pinning muss der Pin zusätzlich noch definiert werden:
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* you need to define the pinning in ''pinning/hardware/<your board>.m4'':
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<code>pin(FREQCOUNT_PIN, PB0, INPUT)</code>
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  pin(FREQCOUNT_PIN, PB0, INPUT)
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* es ist geplant noch ein Multiplexing mit einem zusätzlichen 74HC251 oder dem Ananlog-Multiplexer (unter Verlust des ADCs) einzubauen
 
  
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== Frequenz ==
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* if you want to measure the frequency of multiple signals, you can multiplex them with one or two 74HC251
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* CPU-Ticks von Rising-Edge zu Rising-Edge werden gemessen
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* define the pinning for the control lines you need like this:
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* Minimal das kleinere von 1 Hz und CPU-Frequenz / 16777216, in der Praxis 2 Hz
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  pin(FREQCOUNT_CHANNEL_MULTIPLEX_BIT1, PB1, OUTPUT)
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* Maximal ca. 50 CPU-Takte, also ca. 400KHz bei 20 MHz
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  pin(FREQCOUNT_CHANNEL_MULTIPLEX_BIT2, PB2, OUTPUT)
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* Ist die Frequenz höher, wird dies nicht sicher erkannt, es werden einfach falsche Werte gemessen
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  pin(FREQCOUNT_CHANNEL_MULTIPLEX_BIT2, PB3, OUTPUT)
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* Steigt die Interrupt-Last der CPU (z.B. durch Netzwerkverkverkehr oder UART), sinkt die maximal sicher messbare Frequenz
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  pin(FREQCOUNT_CHANNEL_MULTIPLEX_CS_A, PB4, OUTPUT)
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* Die Frequenz wird intern als Anzahl der Ticks (32 Bit unsigned int) gespeichert
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  pin(FREQCOUNT_CHANNEL_MULTIPLEX_CS_B, PB5, OUTPUT)
  
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== Duty-Cycle ==
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== Frequency ==
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* Kann auch den Duty-Cycle eines PWM-Signals messen
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* CPU ticks from rising edge to rising edge are measured
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* Duty-Cycle ist (Zeit von Rising Edge zu Falling Edge) / Gesamtdauer des letzten Zyklus von Rising zu Rising
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* minimum frequency is the smaller value of 1 Hz and CPU frequency divided by 16777216, in practice 2 Hz
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* Frequenz und Duty-Cycle werden nacheinander gemessen
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* if the frequency is below the minimum, the output is 0
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* Sollte sich die Frequenz signifikant ändern, ist die Duty-Cycle Messung falsch
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* maximum frequency is about 50 cpu ticks, about 400 KHz at 20 MHz CPU
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* Der Duty Cycle wird intern als 8 Bit Wert gespeichert
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* if the frequency is above the maximum you get bogus results
 +
* when the irq load of the cpu increases (e.g. by network traffic or UART), the maximum frequency decreases
 +
 
 +
== Duty Cycle ==
 +
* you can also measure the duty cycle of a PWM signal
 +
* duty cycle is (time from rising edge to falling edge) / time of whole cycle from rising to rising
 +
* frequency and duty cycle are measured one after another
 +
* when the frequency changes significantly the measured duty cycle will be wrong
 +
* duty cycle is stored as 8 bit value
  
 
== Durchschnittsbildung ==
 
== Durchschnittsbildung ==

Revision as of 21:15, 6 November 2011

Language

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Frequency Counter
Status
Stable
menuconfig Applications->Frequency Counter
Pinning yes
Ecmd yes
Depends on ECMD (optional)
Requires -
Code https://github.com/ethersex/ethersex/tree/master/services/freqcount

Measures the frequency and duty cycle of a signal

Pinning

  • the signal must always be fed to the ICP1-pin. Look up in the datasheet which physical pin this is on the used controller.
  • you need to define the pinning in pinning/hardware/<your board>.m4:
 pin(FREQCOUNT_PIN, PB0, INPUT)
  • if you want to measure the frequency of multiple signals, you can multiplex them with one or two 74HC251
  • define the pinning for the control lines you need like this:
 pin(FREQCOUNT_CHANNEL_MULTIPLEX_BIT1, PB1, OUTPUT)
 pin(FREQCOUNT_CHANNEL_MULTIPLEX_BIT2, PB2, OUTPUT)
 pin(FREQCOUNT_CHANNEL_MULTIPLEX_BIT2, PB3, OUTPUT)
 pin(FREQCOUNT_CHANNEL_MULTIPLEX_CS_A, PB4, OUTPUT)
 pin(FREQCOUNT_CHANNEL_MULTIPLEX_CS_B, PB5, OUTPUT)

Frequency

  • CPU ticks from rising edge to rising edge are measured
  • minimum frequency is the smaller value of 1 Hz and CPU frequency divided by 16777216, in practice 2 Hz
  • if the frequency is below the minimum, the output is 0
  • maximum frequency is about 50 cpu ticks, about 400 KHz at 20 MHz CPU
  • if the frequency is above the maximum you get bogus results
  • when the irq load of the cpu increases (e.g. by network traffic or UART), the maximum frequency decreases

Duty Cycle

  • you can also measure the duty cycle of a PWM signal
  • duty cycle is (time from rising edge to falling edge) / time of whole cycle from rising to rising
  • frequency and duty cycle are measured one after another
  • when the frequency changes significantly the measured duty cycle will be wrong
  • duty cycle is stored as 8 bit value

Durchschnittsbildung

  • Durch Interrupt-Verzögerungen etc. kann es zu Fehlmessungen kommen
  • Bei höheren Frequenzen sinkt die maximal mögliche Auflösung
  • Um das zu kompensieren wird immer der Durchschnitt von n Messungen verwendet, n ist im Konfigurationsmenü einstellbar
  • Zusätzlich wird immer der höchste und der niedrigste Wert einer dieser Durchschnittsreihen verworfen (es werden n+2 Samples genommen)

ECMD-Befehle

Hinweis: Channel ist momentan immer 0
Kommando Funktion
fc freq Channel Gibt die Frequenz in Hz zurück (Achtung: 32 Bit).
fc ticks Channel Gibt die Frequenz in CPU Ticks zurück (Achtung: 32 Bit).
fc duty Channel Gibt den Duty Cycle als 8 Bit Wert zurück (0-255 dezimal).
fc %duty Channel Gibt den Duty Cycle in Prozent zurück.
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