C Meter click

Description

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 
2 #include 
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