Howto to display temperature values with decimal places in the chart widget=
ESP32
8.2
Chart widget: Displaying temperature values with 1 decimal place on the y axis for example 20.0 to 20.9
tried to multiply by 10 and add values, but how to scale the values
Hi @steff ,
Here is a complete example which logs a random temperature every minute for a 24 hour period. It also shows you how to set the ticks on the axis as this can be tricky if you haven’t seen it before. If you paste this in the simulator and call the make_chart() function it will update every 250ms where 250ms is equivalent to 1 minute of time on the chart. Here is the code:
#define NUM_HIST_X_LABELS 25
#define NUM_HIST_Y_LABELS 13
#define MINUTES_IN_A_DAY 1440
#define CHART_HEIGHT 410
#define CHART_WIDTH 610
static char *history_x_buf[NUM_HIST_X_LABELS];
static char *history_y_buf[NUM_HIST_Y_LABELS];
static lv_obj_t *chart_history;
static lv_chart_series_t *series_history;
static lv_coord_t history[MINUTES_IN_A_DAY];
static void hist_chart_event_cb(lv_event_t * e) {
lv_obj_draw_part_dsc_t * dsc = lv_event_get_draw_part_dsc(e);
if(!lv_obj_draw_part_check_type(dsc, &lv_chart_class, LV_CHART_DRAW_PART_TICK_LABEL)/* || (dsc->value > 4)*/) return;
static int32_t idx = NUM_HIST_Y_LABELS-1;
if(dsc->id == LV_CHART_AXIS_PRIMARY_Y && dsc->text) {
lv_snprintf(dsc->text, dsc->text_length, "%s", history_y_buf[idx]);
if( --idx == -1 ) idx = NUM_HIST_Y_LABELS-1;
} else if(dsc->id == LV_CHART_AXIS_PRIMARY_X && dsc->text) {
lv_snprintf(dsc->text, dsc->text_length, "%s", history_x_buf[dsc->value]);
}
}
static double random_temperature( void ) {
double range = -120;
range *= ((double)rand()/(double)(RAND_MAX));
range += 100; // generate random temperature between -20 and 100
printf( "temperature:%f\n", range);
fflush(stdout);
return( range );
}
static void update_chart( lv_timer_t * timer ) {
static uint16_t idx = 0;
lv_coord_t chart_value = (lv_coord_t)((random_temperature()+20) * 10); // get a random temperature and scale it to our chart
printf( "scaled for chart:%d\n", chart_value);
fflush(stdout);
lv_chart_set_value_by_id(chart_history, series_history, idx % MINUTES_IN_A_DAY , chart_value );
idx++;
}
static void make_chart( void ) {
double ticks;
int32_t i_pnt;
chart_history = lv_chart_create(lv_scr_act());
lv_obj_set_style_text_font (chart_history, &lv_font_roboto_8, LV_PART_MAIN | LV_STATE_DEFAULT);
lv_obj_set_size(chart_history, CHART_WIDTH, CHART_HEIGHT);
lv_obj_align(chart_history, LV_ALIGN_BOTTOM_MID, 28, -50);
lv_chart_set_type(chart_history, LV_CHART_TYPE_LINE);
lv_chart_set_range(chart_history, LV_CHART_AXIS_PRIMARY_Y, 0, 1200 );
lv_chart_set_div_line_count(chart_history, 13, 25);
lv_chart_set_update_mode(chart_history, LV_CHART_UPDATE_MODE_CIRCULAR); //LV_CHART_UPDATE_MODE_SHIFT
lv_chart_set_axis_tick(chart_history, LV_CHART_AXIS_PRIMARY_X, 10, 5, 25, 1, true, 50);
lv_chart_set_axis_tick(chart_history, LV_CHART_AXIS_PRIMARY_Y, 10, 5, 13, 5, true, 30);
/*Add a data series*/
series_history = lv_chart_add_series(chart_history, lv_palette_main(LV_PALETTE_RED), LV_CHART_AXIS_PRIMARY_Y);
lv_obj_set_style_line_width(chart_history, 1, LV_PART_INDICATOR);
lv_obj_set_style_size(chart_history, 0, LV_PART_INDICATOR);
lv_chart_set_ext_y_array(chart_history, series_history, history);
lv_chart_set_point_count(chart_history, sizeof(history)/sizeof(history[0]));
lv_obj_update_layout(chart_history);
// These never change so just set them the first time...
i_pnt = 0;
int32_t i = NUM_HIST_Y_LABELS-1;
char buf[40];
for( ticks=100; ticks >= -30; ticks-= 10 ) {
i_pnt = snprintf( buf, sizeof(buf), "%6.1f", ticks );
history_y_buf[i] = malloc(i_pnt);
strcpy( history_y_buf[i--], buf );
}
for( int iticks = 0; iticks < NUM_HIST_X_LABELS; iticks++ ) {
i_pnt = snprintf( buf, sizeof(buf), "%02d\n", iticks );
history_x_buf[iticks] = malloc(i_pnt);
if( iticks < 24 ) strcpy( history_x_buf[iticks], buf );
else history_x_buf[iticks][0] = 0;// Set Null string for last tick
}
lv_obj_add_event_cb(chart_history, hist_chart_event_cb, LV_EVENT_DRAW_PART_BEGIN, NULL);
lv_timer_create((void*)update_chart, 250, NULL ); // Update the chart periodically
}
Hopefully you will be able to see how to do things from this example.
Kind Regards,
Pete
Thank you for your effort, in fact it is essentially what I wanted to do.
But… Unfortunately the program crashes on my hardware and in the simulator.
char buf[40];
for( ticks=100; ticks >= -30; ticks-= 10 ) {
i_pnt = snprintf( buf, sizeof(buf), "%6.1f", ticks );
history_y_buf[i] = malloc(i_pnt);
strcpy( history_y_buf[i--], buf );
}
the first strcpy fails?
strange…
for( ticks=100; ticks > -30; ticks-= 10 ) {
i_pnt = snprintf( buf, sizeof(buf), "%6.1f", ticks );
printf ("i_pnt = %d, buf = '%s'\n", i_pnt, buf);
gives me for the first iteration
i_pnt = 6, buf = ’ 100.0’
notice the ‘blank’ before the ‘100’!!!
In the next step, not enough bytes are reserved by ‘malloc’.
Same problem for the y-axis
I ‘fixed’ it by ‘malloc(8)’
ticks >= -30; results in ‘out of bounds’ therefore I changed to ‘ticks > -30’
Pete, thank you for the example!!!
Hi @steff ,
Sorry I think I made a mistake, the malloc should be i_pnt +1 to allow for the terminating NULL… My bad!
I am glad it has enabled you to make progress!
Kind Regards,
Pete