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:
- 0:c5bcf643a8b1
- Child:
- 1:e2034bcdb101
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp Sun Feb 03 21:06:02 2013 +0000
@@ -0,0 +1,32 @@
+#include "mbed.h"
+
+Serial pc(USBTX, USBRX);
+InterruptIn in(p8);
+DigitalOut led(LED1);
+DigitalOut led2(LED2);
+Timer t1;
+
+float t_period = 0; // This is the period between interrupts in microseconds
+float t_freq = 0;
+
+void flip(void)
+{
+ led=!led;
+ t_period = t1.read_us(); // Get time since last interrupt
+ t_freq = (1/t_period)*1000000; // Convert period (in us) to frequency (Hz)
+ t1.reset(); // Reset timer and wait for next interrupt
+}
+
+int main() {
+ pc.printf("\rStarting frequency counter\n");
+ in.mode(PullDown); // Set the pin to Pull Down mode.
+ in.rise(&flip); // Set up the interrupt for rising edge
+ t1.start(); // start the timer
+
+ while (1) {
+ wait_ms(100);
+ led2=!led2;
+ pc.printf("\rfrq is %d Hz\n", (int)t_freq);
+ }
+
+}
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