Electronic Circuits and Projects Forum

Small point: I don't see +5V and Ground connected to the PIC18F. I know you have power and ground or it could not work.

Originally Posted by EI3HG

The inputs do work, but seem to 'sink' the voltage on the input when approaching 5 volts. Also unconnected inputs seem to vary in sympathy with the voltage applied to connected input.

The only time I have seen this is when the pins have been set to output and low. The ADC will still work but the readings are biased towards zero.

Have you tried reading the pin voltages with a multimeter?

Mike.

Hi All,

Thanks for the replies.

It seems from the datasheet quoted above that the source impedance should be below 2k7, so I am close to this with my test Jig, depending on the setting of the pot(2k pots with 2k2 series resistor). However, other suggestions, such as Burt's above (10k pot and 470 R series) would have a higher source impedance. (but other PICs can cope with higher source impedance

The PIC is programmed in 'C' , and I have enlisted some help to do this, (basically I am an analoge guy struggling to get digital!) but here is the code relating to the inputs. there is some other codealso to do with the up/down buttons, BTW the pull up resistors on them are 27K, don't think it's on the drawing, also missing is the 5v and ground connections to the PIC itself, but as someone said above, it is working, in that the display is functioning and the up/down buttons working as required.

My main worry is how to test it properly and what value series resistor do I eventually need when measuring the like of PSU voltages - I don't think there will be a source impedance issue there!. On the other hand, for the forward and reflected power, I may need an Op-Amp there , as I am not sure what the source impedance will be for the directional coupler.
The caps from the inputs to ground I will try - any suggestionson values? as someone said, the reaction times to the inputs doesn't need to be in the microseconds, up to a second or so is fine, except perhaps for the reflected power which needs to b ea little bit faster, tens or hundreds of mS perhaps.

With regard to the DAC, I did consider using a PWM design , but decided against it after discussion and research suggested it may cause the attenuation level to 'cycle and not be precise enough if cap values change over time etc. I was considering using a DAC chip, but have the outputs available on the PIC, and it allows me to choose the bit resolution I need - I may revisit this one day though.

Andy

#pragma config WDT = OFF
//enables the PGM/PGC/PGD pins
#pragma config LVP = OFF
#pragma config PWRT = OFF

#pragma config BOREN = OFF
#pragma config PBADEN = OFF

void InterruptHandlerHigh (void);

long ticks = 0;
long debounce_tick = 0;
unsigned char enter_flag = 0;
unsigned char up_flag = 0;
unsigned char down_flag = 0;
unsigned char draw = 0;
unsigned char current_menu = 2;
unsigned char changing_menus = 0;
char DAC_byte = 0;
BYTE db_store = 10;

//0 - forward power
//1 - reflected power
//2 - MAIN PSU voltage
//3 - Aux PSU voltage
//4 - PA Heat Sink Temp
//5 - PA current
//6 - IPA current
#pragma udata udata5
float v_0;
#pragma udata udata5
float v_1;
#pragma udata udata6
float v_2;
#pragma udata udata6
float v_3;
#pragma udata udata7
float v_4;
#pragma udata udata7
float v_5;
#pragma udata udata8
float v_6;
#pragma udata udata8
float v_7;
#pragma udata udata9
float v_8;
#pragma udata udata9
float v_9;


menu top_menu;
menu power_adj_menu;
menu display_param_menu;

void output_byte_to_DAC(BYTE out)
{
DAC_b8 = (out&0x80)>>7;
DAC_b6 = (out&0x20)>>5;
DAC_b5 = (out&0x10)>>4;
DAC_b4 = (out&0x08)>>3;
DAC_b3 = (out&0x04)>>2;
DAC_b2 = (out&0x02)>>1;
DAC_b1 = (out&0x01);
DAC_b7 = (out&0x40)>>6;
}

void initMCU(void)
{
//set clock to 32 Mhz
OSCCON= 0b01110000;
OSCTUNE = 0b01000000;
INTCON = 0b10100000;
INTCON2 = 0b00000101;
TMR0H = 0; //clear timer
TMR0L = 0; //clear timer
T0CON = 0x80; //set up timer0 - prescaler 1:8

TRISA = 0x1F;
TRISE = 0x07; //direction output
TRISD = 0x00;
TRISC = 0x00;
TRISB = 0xF7;
}

void debounce(void)
{
static int up_button_cycles = 0;
static int down_button_cycles = 0;
static int enter_button_cycles = 0;
if(debounce_tick > 0)
{
//button up logic
if(button_up == 1)
{
up_button_cycles = 0;
}
else
up_button_cycles++;
if(up_button_cycles == 3)
{
up_flag = 1;
}
else if(up_button_cycles > 5)
up_button_cycles = 5;

//button down logic
if(button_down == 1)
{
down_button_cycles = 0;
}
else
down_button_cycles++;
if(down_button_cycles == 3)
{
down_flag = 1;
}
else if(down_button_cycles > 5)
down_button_cycles = 5;

//button enter logic
if(button_enter == 1)
{
enter_button_cycles = 0;
}
else
enter_button_cycles++;
if(enter_button_cycles == 3)
{
enter_flag = 1;
}
else if(enter_button_cycles > 5)
enter_button_cycles = 5;
debounce_tick = 0;
}
}


WORD ADCread(BYTE source)
{
WORD result = 0;
ADCON0 = source << 2;
ADCON0 = ADCON0 | 0x03; //enable A/D convert
while((ADCON0&0x02)!= 0x00);
result = ADRESH;
result = result<<8;
result = result | ADRESL;
ADCON0 = 0;
return result;
}

void ADCinit()
{
//enable all a/d pins and make the voltage reference based on the power pins to the PIC
ADCON1=0x00;
//right justified results
//use a sampling rate of oscilator/32
//us 2 T_ad
ADCON2=0b10001010;
}

void main (void)
{
int read_vals = 0;
int lit = 1;
WORD result;
initMCU();
initMCU_OLED();
oledinit();
ADCinit();
LED = 0;
draw = 1;

top_menu.num_items = 2;
top_menu.selected_item = 0;
top_menu.scrolled_item = 0;
display_param_menu.num_items=9;
display_param_menu.selected_item = 0;
display_param_menu.scrolled_item = 0;
power_adj_menu.num_items = 2;
power_adj_menu.selected_item = 0;
power_adj_menu.scrolled_item = 0;
for(;;)
{
if(ticks > 1)
{
//output_byte_to_DAC(0xAA);
if(read_vals > 10)
{
read_vals = 0;
result = ADCread(0);
v_0 = result/1024.0;
v_0 = (AD0UPPERVAL-AD0LOWERVAL) * (v_0*v_0*AD0QUADRATIC_A + v_0*AD0QUADRATIC_B + AD0QUADRATIC_C)+AD0LOWERVAL;
result = ADCread(1);
v_1 = result/1024.0;
v_1 = (AD1UPPERVAL-AD1LOWERVAL) * (v_1*v_1*AD1QUADRATIC_A + v_1*AD1QUADRATIC_B + AD1QUADRATIC_C)+AD1LOWERVAL;
result = ADCread(2);
v_2 = result/1024.0;
v_2 = (AD2UPPERVAL-AD2LOWERVAL) * (v_2*v_2*AD2QUADRATIC_A + v_2*AD2QUADRATIC_B + AD2QUADRATIC_C)+AD2LOWERVAL;
result = ADCread(3);
v_3 = result/1024.0;
v_3 = (AD3UPPERVAL-AD3LOWERVAL) * (v_3*v_3*AD3QUADRATIC_A + v_3*AD3QUADRATIC_B + AD3QUADRATIC_C)+AD3LOWERVAL;
result = ADCread(4);
v_4 = result/1024.0;
v_4 = (AD4UPPERVAL-AD4LOWERVAL) * (v_4*v_4*AD4QUADRATIC_A + v_4*AD4QUADRATIC_B + AD4QUADRATIC_C)+AD4LOWERVAL;
result = ADCread(5);
v_5 = result/1024.0;
v_5 = (attenuator_db_high-attenuator_db_low)*(v_5*v_5*AD5QUADRATIC_A + v_5*AD5QUADRATIC_B + AD5QUADRATIC_C)+attenuator_db_low;
result = ADCread(6);
v_6 = result/1024.0;
v_6 = (AD6UPPERVAL-AD6LOWERVAL) * (v_6*v_6*AD6QUADRATIC_A + v_6*AD6QUADRATIC_B + AD6QUADRATIC_C)+AD6LOWERVAL;
result = ADCread(7);
v_7 = result/1024.0;
v_7 = (AD7UPPERVAL-AD7LOWERVAL) * (v_7*v_7*AD7QUADRATIC_A + v_7*AD7QUADRATIC_B + AD7QUADRATIC_C)+AD7LOWERVAL;
//v_5 is going to be SWR, but it was forward voltage
v_9 = (v_6 + v_7)/(v_6 - v_7);
result = ADCread(8);
v_8 = result/1024.0;
v_8 = (AD8UPPERVAL-AD8LOWERVAL) * (v_8*v_8*AD8QUADRATIC_A + v_8*AD8QUADRATIC_B + AD8QUADRATIC_C)+AD8LOWERVAL;
// result = ADCread(9);
// v_9 = result/1024.0;
// v_9 = (AD9UPPERVAL-AD9LOWERVAL) * (v_9*v_9*AD9QUADRATIC_A + v_9*AD9QUADRATIC_B + AD9QUADRATIC_C)+AD9LOWERVAL;
}
controller_update();
menu_draw();
ticks = 0;
read_vals++;
}
debounce();
menu_update();
}
}


#pragma code InterruptVectorHigh = 0x08
void
InterruptVectorHigh (void)
{
_asm
goto InterruptHandlerHigh //jump to interrupt routine
_endasm
}

//----------------------------------------------------------------------------
// High priority interrupt routine

#pragma code
#pragma interrupt InterruptHandlerHigh

void
InterruptHandlerHigh ()
{
unsigned char changes, portbd;
static unsigned char last_portb;

//probably don't need this
if(INTCONbits.RBIF != 0)
{
portbd = PORTB;
INTCONbits.RBIF = 0;
}

//need this
if (INTCONbits.TMR0IF)
{
//check for TMR0 overflow
INTCONbits.TMR0IF = 0; //clear interrupt flag
ticks++;
debounce_tick++;
}
}