Satoru Yoshida
measure ohm of HS15P
Fork of
Frequency_counter
by 
Neel Shah
This test program measures ohm of HS15P, humidity sensor.
| C(micro F) with LMC555 | 0.1 | 0.15 | 0.22 | 0.33 | 0.47 | 0.68 | 1 |
| CONV_KILO_OHM | 0.0072 | 0.0048 | 0.0033 | 0.0022 | 0.0015 | 0.0011 | 0.00072 |
If you get 2500 microseconds as interrupt time interval , it means 18 kilo ohm when 0.1 micro F. ( = 2500 * 0.0072 )
- ohm of HS15P is calculated from pulse interval of LMC555.
- CONV_KILO_OHM will be used.
- this program reads interval time.between interrupt in the P8.
- takes ON the P9 to oscillate LMC555 as short as enough to measure interval time
- last several interval times will be used for calculation.
- the time is defined as READ_TIMER .
- In current circit, VDD of LMC555 is about 1.55V, AC 0.4V between pins of HS15P.
- LMC555 consumes 120 micro A while oscillation, 90 micro A when level of P9 is OFF. (reset is ON)
- Total 1-2mA is consumed in the circit.
Related nootbook : https://mbed.org/users/strysd/notebook/measure_humidity_with_hs15p_and_lmc555/
Diff: main.cpp
- Revision:
- 3:bf0a5effbed2
- Parent:
- 2:c4d4f0f9d77c
- Child:
- 4:64d9c0bed75b
--- a/main.cpp Sat Jun 01 07:49:57 2013 +0000
+++ b/main.cpp Mon Jun 03 12:36:37 2013 +0000
@@ -2,8 +2,8 @@
//see mbed.org/users/strysd/notebook/measure_humidity_with_hs15p_and_lmc555/
#define ohm_constant 7.2 //if use 0.1 micro F
+#define in_limit 20 //limit of interrupt times
-Serial pc(USBTX, USBRX);
InterruptIn in(p8);
DigitalOut vcc555(p9);
DigitalOut led(LED1);
@@ -12,15 +12,16 @@
float t_period = 0;//between interrupts in microseconds
float my_freq = 0;//Hz
float my_ohm = 0;//ohm for HS15P
-int in_limit = 10;
-int in_count = 0;
+int in_count = 0;//interrupt times
void flip(void)
{
if(in_count > 0){
- t_period = t1.read_us();// Get time since last interrupt
+ if(in_count > 15){
+ t_period = t1.read_us();// Get time since last interrupt
+ }
+ t1.reset();// Reset timer and wait for next interrupt
in_count--;
- t1.reset();// Reset timer and wait for next interrupt
} else {
//No use interrupt
vcc555 = led = 0;
@@ -34,24 +35,28 @@
in.mode(PullUp);
in.rise(&flip);// Set up the interrupt for rising edge
- pc.printf("\rStarting measure\n");
+ printf("\rStarting measure\n");
while (1) {
//Use interrupt
+ t_period = 0;
t1.start();
in_count = in_limit;
vcc555 = led = 1;
wait_ms(200);
-
- if (t_period > 0){
- my_freq = (1000/t_period)*1000; // Convert to Hz
- my_ohm = t_period * ohm_constant;// Convert to ohm
-
- pc.printf("\r %d Hz, %d micro sec, %d ohm \n",
- (int)my_freq, (int)t_period, (int)my_ohm);
+
+ if (t_period < 20 || t_period > 100000){
+ //< 20 micro sec (> 50 kHz)
+ //> 0.1 sec (< 10 Hz)
+ printf("\r not ready\n");
+ wait_ms(5000);
} else {
- pc.printf("\r not ready\n");
+ my_freq = 1000000/t_period;// Convert to Hz
+ my_ohm = t_period * ohm_constant / 1000;// Convert to kilo ohm
+ printf("\r %d Hz, %d micro sec, %4.1f kilo ohm \n",
+ (int)my_freq, (int)t_period, my_ohm);
}
- wait_ms(1800);
+
+ wait_ms(4800);
}
}
\ No newline at end of file