#Diptrace 2.9 beta code
#Diptrace 2.9 beta free

Then 'source' is set to 1, to start charging the capacitor, and a timer is started. 'source' should initially be set to 0 to keep the capacitor discharged (remember, the C programming language does not initialize numerical variables to 0 as some other languages do, so you have to do it). Another variable, 'capacitor', of type AnalogIn, has its pin wired to the junction of the capacitor and resistor.

#Diptrace 2.9 beta free

That pin is wired to the free end of the resistor. For charging/discharging, I defined a variable named 'source' of type DigitalOut. It discharged the capacitor through the same large-value resistor used for charging. My first version did not use a dischage pin. Today I wired up the capacitance meter circuit. I would have used a couple of transistors, but the DigitalOut/In switching, if it works, is much easier. That is being done to achieve switching action. Having not personally built the circuit, I am curious about how well changing a pin from DigitalOut to DigitalIn and back again works. If Vout is a little high, say 3.35 V, the same applies the capacitor has still charged to 63% of the supply, and the time represents one RC time constant. The beauty is that if Vout varies a little (or even a lot), say to 3.28 V, the capacitor has still charged to 63% of that. Then divide the time by the resitance to get the capacitance.

That means all you have to do is time how long it takes to go from 0.0 to 0.63, and that is one RC time constant. That is, it does not measure voltage in volts, but instead gives a reading that is a decimal fraction of Vout (nominally 3.3 V), so readings will vary from 0.00 to 0.99, or possibly 1.0. The neat thing about AnalogIn is that it is ratiometric. I would drive the resistor and capacitor with a DigitalOut and read the capacitor with an AnalogIn, just as the Arduino link shows. Interesting little circuit, using the mbed. Not sure whether I screwed up wiring up my breadboard, in my code, or both.Īny tips, thoughts, or information would be very much appreciated.

The problem I have is that as soon as the charge pin comes on, the voltage read pin 'sees' the 3.3 V and assumes the capacitor is charged, then turns off.

#Diptrace 2.9 beta code

I carefully followed the schematic as closely as I could, and wrote some code to measure the voltage on the capacitor if the capacitor is close to 0V, then my code turns on a DigitalOut pin to charge it up. I found something for an Arduino here: and tried to build that. I would like to build a capacitance meter. I'm impressed and excited to hone my skills and have spent a ton of my spare time learning more about electronics. I've also hooked up a 40x4 LED display and that works (mostly) fine. I've built a nice little power supply that takes 9V in from a wall-wart and brings it down to a nice 5V to run the Mbed. I've so far done some little projects with the Mbed, including Hello World, a bunch of 'blink or dim these LEDs' projects, a basic voltmeter (amazingly accurate on an 'AA' cell), and so on. This is when I found Mbed and ordered one. I started reading about the great number of people that are transitioning from 8-bit up to 32-bit micro-controllers and then I started reading up on the LPC Expresso boards. I had read online about all the fun that people are having with Arduino, and was inspired. I've taken some C courses, but that was too long ago to think about. I've been programming for a couple of decades, mostly in Perl, PHP, and so on. I'm new here, and fairly new to electronics.