![]() Have an accurate reference then use fixed capacitors. The capacitors can bothīe fixed unless you want to tune it using a frequency reference. The crystal oscillator is simply a crystal and two capacitorsĬonnected to the PIC oscillator port at OSC1 and OSC2. The segment enable lines to control the character displayed. This lets the micro turn on each display sequentially. Outputs of the 4017 are connected to the common cathode of each seven segmentĭisplay. Port Aĭrives the reset line and clock signal to the 4017 and transistors at the The 8 seven segment displays are multiplexed using a JohnsonĬounter (4017) that activates a single output after each clock pulse. The main circuit blocks of the frequency counter circuit are PIC frequency counter circuit using 7 segment displays, The hex file is contained in the download.įor the general theory of operation of this circuit and notes You can recompile the frequency counter circuit files if you want examineĬode operation (using the built in simulator) or change the source code. �Just observe each digit and make sure it goesįor a tutorial on compiling these files click Test wiring 2 : Outputs a shifted digit set from 1-8 to test PORTDĬonnections to each 7 segment. �You can use this test to see if PORTDĪnd each transistor driver is connected correctly. Test wiring 1 : Outputs�constant digits to the display and These tests will also test out a system using individual 7 if the 1st download file does not appear to work: Once constructed you can test the wiring out using theįollowing two files e.g. Note: Check your email for the project code download Hardware level Intermediate Hardware notes Seven segment multiplexing. Compiler Mikroelectronika MikroC Compiler Free! Target 16F877A (retargetable to other PICs that have TMR1) Software level Advanced. Note: The exact maximum operating frequency is determined by ![]() Second measurement time gives a frequency resolution of 1 Hz. Just as in the LCD project the measurement time is 1 second theįinal count is actually the frequency of the input signal and again using the 1 The extra 0.25 indicates 64 cycles are required before the last interruptĬalculations as it is exactly the same in operation. Since the overflow occurs every time that the counter passes 256 we need to Timer 0 counter overflows every 256 counts. To get to 1 second we need 1/(Fosc/4) counts = 1/ 1e-6 = 1e6 Main clock processing period time = Fosc/4 = (1/(4e6/4)) = 1e-6 = 1us Interrupts generated when an overflow of the counter occurs. (Fosc/4=4e6/4), and as before we use Timer0. To create a capture time of 1 second requires counting the internal clock Input signal level TTL Frequency Counter: Operation Frequency Counter: Specification Min frequency 1Hz Max frequency ~50MHz The complicated bit is that the interrupt routine must be small so that theĬount is captured correctly while still allowing display refresh. (75LS47 or CMOS 4511) but the design here does it all. Normally you would use a TTL chip that does the refreshing for you The other problem with 7 segment displays is that they must be updatedĪpproximately every 20ms for your eye to be fooled into seeing a continuousĭisplay so part of the Timer 0 counting goes into doing 7 segment display Main clock frequency is set by a crystal resonant at 4MHz. In addition Timer 0 is used to obtain anĪccurate period of 1 second by counting 1e6 clock edges (Fsoc/4=1MHz) where the Adding the current value of the counter at ![]() Counter overflows are accumulated to give the Use the frequency counter shown here is extremely useful.Ĭounter project this frequency counter circuit uses TMR1 in 16 bit counter mode ![]() Reciprocal counting displays more digits for more resolutionĪt lower frequency i.e. On the input so for a 1Hz input, the digit 1 is displayed indicating aįrequency of 1Hz. The direct counting method means that the number of digits displayed depends Uses a rising edge event to trigger a counter and stops the counter on a The other way of making a frequency counter is reciprocal counting which Want to obtain a frequency reading) is used to directly increment a counter This PIC frequency counter circuit uses a multiplexed seven segment display to provideĨ digits and uses timer 1 to count edges of the input signal and Timer 0 toįrequency measurement which means that the input event (for which you
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