C Meter click

The chip is implemented in an astable multivibrator circuit with fixed resistors and adjustable capacitors.

The board has four different-sized plates for placing SMD capacitors (covering standard SMD packaging dimensions) as well as a socket for inserting a thru hole capacitor.

The board outputs a square wave frequency through the INT pin. Depending on the capacitor placed on the board, the value of this frequency changes. The value of a capacitor can be inferred using a simple algorithm (shown in the Libstock code example).

Onboard screw terminals are placed to allow the click to be used with multimeter probes.

C Meter click is designed to use a 5V power supply, but can work with either 3.3V or 5V logic levels.

Specification

C Meter click has circuitry for measuring the value of capacitors. The design is based on a NE-555 timer/square-wave generator. The chip is implemented in an astable multivibrator circuit with fixed resistors and adjustable capacitors.

Features and usage notes

C Meter click has four different-sized plates for placing SMD capacitors (covering standard SMD packaging dimensions) as well as a socket for inserting a thru hole resistor. Each plate is labeled with package size in standard imperial measurements:

• 1210 — 3.2mm x 2.5mm
• 1206 — 3.2 mm x 1.6 mm
• 0805 — 2.0 mm x x1.25 mm
• 0603 — 1.6 mm x 0.8 mm

The board outputs a square wave frequency through the INT pin. Depending on the capacitor placed on the board, the value of this frequency changes. The value of a capacitor can be inferred using a simple algorithm (shown in the Libstock code example).

Onboard screw terminals are placed to allow the click to be used with oscillator probes.

C Meter click is designed to use a 5V power supply, but can work with either 3.3V or 5V logic levels.

Programming

This code snippet uses a preset calibration value and finds the capacitance of the capacitor for displaying on the TFT.

  1 #include <stdint.h>
  2 #include <stdbool.h>
  3 #include "resources.h"
  4 
  5 // C_Meter Click
  6 sbit C_METER_RST         at GPIOC_ODR.B2;
  7 sbit C_METER_INT         at GPIOD_ODR.B10;
  8 // TFT module connections
  9 unsigned int TFT_DataPort at GPIOE_ODR;
 10 sbit TFT_RST at GPIOE_ODR.B8;
 11 sbit TFT_RS at GPIOE_ODR.B12;
 12 sbit TFT_CS at GPIOE_ODR.B15;
 13 sbit TFT_RD at GPIOE_ODR.B10;
 14 sbit TFT_WR at GPIOE_ODR.B11;
 15 sbit TFT_BLED at GPIOE_ODR.B9;
 16 
 17 
 18 
 19 void system_setup( void );
 20 void setup_interrupt( void );
 21 void InitTimer2( void );
 22 void display_init( void );
 23 
 24 uint32_t int_count = 0;
 25 uint32_t timer_count_end = 0;
 26 bool sec_flag = false;
 27 
 28 void main() 
 29 {
 30     //Local Declarations
 31 	char uart_text[ 40 ];
 32 	float c_cal = 0.0;
 33 	float t_meas = 0.0;
 34 	float c_meas = 0.0;
 35 	float final = 0.0;
 36 	float t_cal = 0.0;
 37 
 38     system_setup();
 39     setup_interrupt();
 40     InitTimer2();
 41     display_init();
 42     
 43     t_cal = 1.0 / 23350.0;
 44     c_cal = t_cal / 77616.0;
 45     
 46     int_count = 0;
 47 
 48     while(1)
 49     {
 50     
 51         if( sec_flag )
 52         {
 53             //Measurment
 54             t_meas = 1.0 / timer_count_end;
 55             c_meas = t_meas / 77616.0;
 56             final = fabs( c_cal - c_meas );
 57             //Print out
 58             FloatToStr( final, final_text );
 59             TFT_Rectangle( 100, 100, 200, 120 );
 60             TFT_Write_Text( final_text, 100, 100 );
 61             TFT_Write_Text( " Farad", 190, 100 );
 62             //Reset flags
 63             sec_flag = false;
 64             int_count = 0;
 65             timer_count_end = 0;
 66         }
 67     }
 68 }
 69 
 70 void display_init( void )
 71 {
 72     TFT_Init_ILI9341_8bit( 320, 240 );
 73     TFT_BLED = 1;
 74     TFT_Set_Pen( CL_WHITE, 1 );
 75     TFT_Set_Brush( 1, CL_WHITE, 0, 0, 0, 0 );
 76     TFT_Set_Font( TFT_defaultFont, CL_BLACK, FO_HORIZONTAL );
 77     TFT_Fill_Screen( CL_WHITE );
 78     TFT_Set_Pen( CL_BLACK, 1 );
 79     TFT_Line(  20,  46, 300,  46 );
 80     TFT_Line(  20,  70, 300,  70 );
 81     TFT_Line(  20, 220, 300, 220 );
 82     TFT_Set_Pen( CL_WHITE, 1 );
 83     TFT_Set_Font( &HandelGothic_BT21x22_Regular, CL_RED, FO_HORIZONTAL );
 84     TFT_Write_Text( "C Meter click", 105, 14 );
 85     TFT_Set_Font( &Tahoma15x16_Bold, CL_BLUE, FO_HORIZONTAL );
 86     TFT_Write_Text( "C Meter", 135, 50 );
 87     TFT_Set_Font( &Verdana12x13_Regular, CL_BLACK, FO_HORIZONTAL );
 88     TFT_Write_Text( "EasyMx PRO v7 for STM32", 19, 223 );
 89     TFT_Set_Font( &Verdana12x13_Regular, CL_RED, FO_HORIZONTAL );
 90     TFT_Write_Text( "www.mikroe.com", 200, 223 );
 91     TFT_Set_Font( &Tahoma15x16_Bold, CL_BLACK, FO_HORIZONTAL );
 92 }
 93 
 94 void system_setup( void )
 95 {
 96     //GPIO
 97     GPIO_Digital_Output( &GPIOC_BASE, _GPIO_PINMASK_2 );    //RST
 98     GPIO_Digital_Input( &GPIOD_BASE, _GPIO_PINMASK_10 );    //INT
 99 
100     //RST Toggle
101     C_METER_RST = 0;
102     Delay_ms(50);
103     C_METER_RST = 1;
104 
105     //UART
106     UART1_Init( 9600 );
107     UART1_Write_Text( "UART Initializedrn" );
108 
109 }
110 
111 void setup_interrupt( void )
112 {
113   GPIO_Digital_Output(&GPIOE_BASE, _GPIO_PINMASK_HIGH);  // Enable digital output on PORTD
114   GPIOE_ODR = 0xAAAA;
115   GPIO_Digital_Input(&GPIOD_BASE, _GPIO_PINMASK_10);
116 
117   RCC_APB2ENR.AFIOEN = 1;              // Enable clock for alternate pin functions
118   AFIO_EXTICR3 = 0x0300;               // PD10 as External interrupt
119   EXTI_FTSR = 0x00000400;              // Set interrupt on Rising edge
120   EXTI_IMR |= 0x00000400;              // Set mask
121   NVIC_IntEnable(IVT_INT_EXTI15_10);   // Enable External interrupt
122   EnableInterrupts();                  // Enables the processor interrupt.
123 }
124 
125 void ExtInt() iv IVT_INT_EXTI15_10 ics ICS_AUTO 
126 {
127    EXTI_PR.B10 = 1;                             // clear flag
128    int_count++;
129 }
130 
131 void InitTimer2() //1 second
132 {
133   RCC_APB1ENR.TIM2EN = 1;
134   TIM2_CR1.CEN = 0;
135   TIM2_PSC = 1124;
136   TIM2_ARR = 63999;
137   NVIC_IntEnable(IVT_INT_TIM2);
138   TIM2_DIER.UIE = 1;
139   TIM2_CR1.CEN = 1;
140 }
141 
142 void Timer2_interrupt() iv IVT_INT_TIM2 
143 {
144   TIM2_SR.UIF = 0;
145   timer_count_end = int_count;
146   int_count = 0;
147   sec_flag = true;
148 }

Code examples that demonstrate the usage of C Meter click with MikroElektronika hardware, written for mikroC for ARM is available on Libstock

Downloads

 C Meter click Examples 

 C Meter click Schematic