5 replies to this topic

[ncsteinb]

Hey guys, 

I'm having some issues with my program. I connected my scope to the output of the PWM, but I'm only getting a solid 3.3v. Anyone have a Netduino and a scope handy? I need a reality check here...

 

Thanks!

 

P.S. I disabled the adjustments to make life easier?

using System;using System.Net;using System.Net.Sockets;using System.Threading;using Microsoft.SPOT;using Microsoft.SPOT.Hardware;using SecretLabs.NETMF.Hardware;using SecretLabs.NETMF.Hardware.NetduinoPlus;// Uses .NETMF 4.1namespace PWM_Tester{    public class Program    {        public static void Main()        {            AnalogInput Frequency_Pot = new AnalogInput(Pins.GPIO_PIN_A0);            AnalogInput Duty_Pot = new AnalogInput(Pins.GPIO_PIN_A1);            PWM Test_PWM = new PWM(Pins.GPIO_PIN_D5);            while (true)            {                double Freq_Hz_Bits = Frequency_Pot.Read();                double Duty_Cycle_Bits = Duty_Pot.Read();                double Freq_Hz_Scale = Freq_Hz_Bits / 1023; // To scale from 0-1                double Duty_Cycle_Scale = Duty_Cycle_Bits / 1023; // To scale from 0-1                int Duty_Cycle = 50; //(int)(Duty_Cycle_Scale * 100); // To scale from 0-100%                uint PWM_Min = 10; // In Hz                uint PWM_Max = 400; //In Hz                int Freq_Hz = 100; //(int)(PWM_Min + (Freq_Hz_Scale * (PWM_Max - PWM_Min)));                uint period = (uint)((1 / Freq_Hz) * 1000 * 1000); // Period in usec (*microseconds*)                uint duration = (uint)(Duty_Cycle_Scale * period); // Duration in usec                Test_PWM.SetPulse(period, duration);                Debug.Print("Duty Cycle = " + Duty_Cycle + "%");                Debug.Print("Frequency = " + Freq_Hz + "Hz");                Thread.Sleep(100);             }        }    }}

[ncsteinb]

Anyone?? Any input would be nice...

 

Thanks.

[Paul Newton]

Hi,

 

I don't have any hardware to hand right now.

 

I would try calling Test_PWM.SetPulse() with hard coded integer values instead of calculated ones.

 

I am a little suspicious of your calculation (uint)((1 / Freq_Hz) * 1000 * 1000);

I think that since Freq_Hz is an integer, and "1" is an integer, the arithmetic may be integer arithmetic (1 / 100 = 0).

Try "1.0 / Freq_Hz", or make Freq_Hz a float.

 

Hope this helps a bit - Paul

[ncsteinb]

Paul, 

I did hard code it. I 'commented out' the calculations. I saw no change on the output. 

 

I will try playing around with the math. That might just be it. I'll report back here once I complete the test. 

BTW, do you know if the PWM needs a pulldown or a pullup? Is PWM a trigger HIGH or trigger LOW?

 

Thanks

[Paul Newton]

A few observations:

If hard coding the values does not work, then there is something other than the maths wrong.

My understanding (at least for the Netduino Plus v1) is that when you configure a pin as a PWM output, it will be a push/pull output, hence no pullup or pulldown should be required.

PWM is normally active high - so if you give it a pulse of 3/4 of the period, the output will be high for 3/4 of the time.

(If you need it to be active low, then you can change the pulse length in software to be pulse = (period - desired pulse), thus for OFF, you would set the pulse equal to the period, etc.)

 

Which hardware are you using? Netduino Plus v1 or v2

 

Assuming you have a Netduino Plus v1:

I cut this code down from the .netmf v4.1 version of my buggy project, I can't test it on hardware as I have upgraded my Netduino Plus v1's to .netmf v4.2, but it compiles OK, and it would be interesting to see what you get when you run it.

using System.Threading;                       // Thread.Sleepusing SecretLabs.NETMF.Hardware;              // PWM classusing SecretLabs.NETMF.Hardware.NetduinoPlus; // Pins enumerationnamespace PwmTestHarness{    public class Program    {        public static void Main()        {            PWM pwmPort = new PWM(Pins.GPIO_PIN_D5);            pwmPort.SetPulse(20000, 15000);  // period = 20ms - 50Hz, pulse 15ms            while (true)            {                Thread.Sleep(100); // Loop here forever            }        }    }}

Paul

[TinkeringTurtle]

Here's what you get with Paul's sample in case you're still wondering...

 pwm.jpg   106.86KB   7 downloads