Project Questions about Programming and Electrical

[RyanN]

First off, a description of my project:
I started building a contraption that I call the "Weather Alert." It basically houses a 12V battery, microcontroller, switches, LEDs, Power Inverter, 12V outlet, 120V outlet, and integrated flood lights. My last version of this thing used a BS2 controller, but that proved to be very flaky and didn't have enough ports for me to use. Now this one is controlled by using the 2005 robot controller. I have the controller to run continuously in autonomous mode without the Operator Interface so all programming will be done int he autonomous code. Here are my questions:

Since I know nothing of programming, what variable is used to show the battery voltage, and if there is an equation to detect the exact voltage, can you please supply it?

Is there a way to output a frequency to a speaker to use for an alarm? This will have to be capable of producing many different types of sounds.

How would you charge the battery for this? I was thinking of just using a regular 20AMP Headlight relay to connect and disconnect the charger, but if I do this and run the battery completely down and it cannot connect the charger, how would I charge the battery? I can't have it setup on a normally closed circuit either because when I turn the Weather Alert system off, the charger would remain on, killing my battery(ies).

Some additional information:
My power switch is a DPDT Momentary switch. Both poles are used: one gives the system a "jumpstart" so it can come on (Switch gives power to the power relay, which provides power to the whole system), the other pole is used to send the kill signal to the robot controller.

I think I have a way to connect the charger by using some diodes and letting the RC only charge the battery for like 30 seconds if the battery if full or continue to charge it if it is dead.

If this all seems very confusing, it probably is... Just ask me a particular question and I'll answer it to the best of my knowledge.

[DonRotolo]

What source of power is available to charge the battery? If you have 120 AC, then a small charger like the ones used for FIRST would be perfect - leave them on and connected forever and no overcharging.

If it's some other power source, then provide more details please.

Don

[RyanN]

Originally Posted by Don Rotolo

What source of power is available to charge the battery? If you have 120 AC, then a small charger like the ones used for FIRST would be perfect - leave them on and connected forever and no overcharging.

If it's some other power source, then provide more details please.

Don

I want to use something like a 15V 1.5AMP charger (I used a 13.5V 1.5AMP one on my last version) Something that will charge the battery quicker than 3 days. Also, last time I tried leaving the charger on continuously, 3 out of 4 of the batteries cracked and went bad, and I could feel the heat coming out of them with the charger on. So... having a charger that automatically comes on and off is important.

[Phalanx]

Look in ifi_aliases.h, You will find the variables for the battery.
I hope this helps.

/*
*-----------------------------------------------------------------------------------------------------
*---------- Aliases for Battery Voltage bytes --------------------------------------------------------
*-----------------------------------------------------------------------------------------------------
* Formula to calculate voltage in volts:
* current_voltage = battery_voltage * 0.038 + 0.05;
*/

#define battery_voltage rxdata.rc_main_batt*15.64/256
#define backup_voltage rxdata.rc_backup_batt*15.64/256

[RyanN]

Originally Posted by Phalanx

Look in ifi_aliases.h, You will find the variables for the battery.
I hope this helps.

/*
*-----------------------------------------------------------------------------------------------------
*---------- Aliases for Battery Voltage bytes --------------------------------------------------------
*-----------------------------------------------------------------------------------------------------
* Formula to calculate voltage in volts:
* current_voltage = battery_voltage * 0.038 + 0.05;
*/

#define battery_voltage rxdata.rc_main_batt*15.64/256
#define backup_voltage rxdata.rc_backup_batt*15.64/256

Thanks!

Also, I'm going to add something. I think for the charger, I might have a manual override so I can force it to charge while off (like just a small switch in the back)

[Kevin Sevcik]

You could pretty easily use the CCP ports represented by PWMs 13-16 to output single frequency tones. You'd set it up to output a square wave at the particular frequency you want. You'd have to filter it fairly heavily if you wanted a pure tone, of course. Square waves have harmonics at odd multiples of the fundamental frequency, so if it were me, I'd pick what your high frequency is, make yourself something like a 4th or 6th order low pass filter with a corner frequency at that highest frequency. Then you can put out frequencies down to about 1/2 that highest frequency and still have a pretty pure tone. You'd need to make up a separate amp to drive your speaker, and you'd want it to filter out the DC offset inherent in that initial PWM-style square wave and you'd probably need to create a virtual ground split between your 0V and 12V and various other things as well, of course.

[RyanN]

Originally Posted by Kevin Sevcik

You could pretty easily use the CCP ports represented by PWMs 13-16 to output single frequency tones. You'd set it up to output a square wave at the particular frequency you want. You'd have to filter it fairly heavily if you wanted a pure tone, of course. Square waves have harmonics at odd multiples of the fundamental frequency, so if it were me, I'd pick what your high frequency is, make yourself something like a 4th or 6th order low pass filter with a corner frequency at that highest frequency. Then you can put out frequencies down to about 1/2 that highest frequency and still have a pretty pure tone. You'd need to make up a separate amp to drive your speaker, and you'd want it to filter out the DC offset inherent in that initial PWM-style square wave and you'd probably need to create a virtual ground split between your 0V and 12V and various other things as well, of course.

Can you please elaborate? Like I've connected my speaker to a this transistor and I have sound, but it's just a steady pulse, like you would expect from a PWM signal. I really need the help with the programming. I'm electrical, not programming, though I've just learned my first lessons with C like creating variables, the evil semicolon; how to compare things using if {} and how to set variables to certain values. That is literally all I know. I even had trouble compiling the code... (due to something going crazy with MPLAB and not saving my user_routines_fast.c... that took about 20 minutes to figure out). Some coding examples or some electrical schematics of what you are talking about will help a lot. I also have the option to use a Homework Basic Stamp boards as like a sound card, but I'd rather not do that because of the power consumption and the price.

[Kevin Sevcik]

Ryan,

PWM outputs 13-16 are directly connected to the user processor's CCP modules, so you can use them to generate timed pulses. The default code has a section briefly covering this:

/* FIFTH: Set your PWM output types for PWM OUTPUTS 13-16.
  /*   Choose from these parameters for PWM 13-16 respectively:               */
  /*     IFI_PWM  - Standard IFI PWM output generated with Generate_Pwms(...) */
  /*     USER_CCP - User can use PWM pin as digital I/O or CCP pin.           */
  Setup_PWM_Output_Type(IFI_PWM,IFI_PWM,IFI_PWM,IFI_PWM);

  /* 
     Example: The following would generate a 40KHz PWM with a 50% duty cycle on the CCP2 pin:

         CCP2CON = 0x3C;
         PR2 = 0xF9;
         CCPR2L = 0x7F;
         T2CON = 0;
         T2CONbits.TMR2ON = 1;

         Setup_PWM_Output_Type(USER_CCP,IFI_PWM,IFI_PWM,IFI_PWM);
  */

One use for the CCP hardware was replacing the IFI code for the PWMs with more stable code. This is described here.

So, using the CCP, you can get a square wave signal at (mostly) whatever frequency you want, but two problems remain. First, the signal will oscillate between 0(ish)V and 5(ish)V. Sending something like this through a speaker isn't particularly nice. Especially if the 0V side isn't 0V, as then you'd be constantly sending a current through the speaker. So you'd need an op-amp circuit to shift the square wave so it oscillates around 0V.

You could, in fact, send this through the speaker, but it'd sound a bit odd as it's not a nice sine wave like a pure audio tone is. It's possible to get a nice pure tone out of a square wave, however. The sharp edges (more or less) represent higher frequency components of the signal. So if you create a filtering circuit to filter out high frequencies, you'll get a much purer, cleaner tone. That bit isn't as necessary to making a sound come out of the speaker, though.

[RyanN]

Thanks. I'll try to figure it all out this weekend. I just got a bunch of stuff working on it until a PWM cable randomly decided to go out or else a pin on the circuit board came loose and is not giving me a good connection. I think I may just try to move it to a different pin.

[Alan Anderson]

Originally Posted by Kevin Sevcik

Sending something like this through a speaker isn't particularly nice. Especially if the 0V side isn't 0V, as then you'd be constantly sending a current through the speaker. So you'd need an op-amp circuit to shift the square wave so it oscillates around 0V.

You can block DC current by putting a suitable capacitor in series with the speaker. That's not always a perfect option, but it's certainly a lot easier, cheaper, and quicker than adding active circuitry that requires a bipolar power supply.

[Al Skierkiewicz]

Ryan,
Audio alerts can take many different forms. If you are trying to get someone's attention, a Sonalert or Piezo electric transducer works very well. These devices work best at their resonant frequency but can reproduce a range of frequencies in the mid band of human hearing. They are easy to interface and are pretty cheap. I have a used a few from Radio Shack like the ones here...http://www.radioshack.com/family/ind...032058.2032230

[RyanN]

Originally Posted by Al Skierkiewicz

Ryan,
Audio alerts can take many different forms. If you are trying to get someone's attention, a Sonalert or Piezo electric transducer works very well. These devices work best at their resonant frequency but can reproduce a range of frequencies in the mid band of human hearing. They are easy to interface and are pretty cheap. I have a used a few from Radio Shack like the ones here...http://www.radioshack.com/family/ind...032058.2032230

I'm looking for something that would have a variety of different tones to play for different alarms. Like an alarm for a power outage, flood waters, high winds, temperature, and other related types of warnings. I'm used to a basic stamp (freqout) where I can customize my sounds. I'm thinking of using one like a sound card and using the pulsin command to figure out what type of alarm to do, but I'd rather still just do it all within the RC.

[Kevin Sevcik]

Ryan, again, you can customize the CCP output to produce different frequencies. Not a LOT if you want it to sound half decent, but still probably 3-4 distinct tones. Honestly, with just two tones and a little clever programming you could get several different signals by pulsing and alternating the tones at intervals, sort of like morse code or the BIOS beep codes computers use.

Addressing Alan's comments, yes putting a capacitor in series with your amplifier or speaker would remove the DC component of the signal, but if you're planning on using a bipolar amplifier of some sort to power your speaker, then I'd recommend the extra trouble of a little active filtering, as it would really help in the long run. What I wouldn't recommend is running he speaker directly from the RC digital output. I don't think they can source or sink nearly enough current to work well in that application.

[Al Skierkiewicz]

Ryan,
You can use piezo buzzers in place of speakers. They are easy to interface and can play out a band of frequencies. At least one of the Radio Shack devices is listed as midband 1500-3000Hz. That is certainly enough to give you R2D2 like sounds. They are very efficient giving upwards of 90dB+ outputs at 10-15 ma. Most can be used as the collector load in a simple one transistor amp. Since the current demands are low, a 2N2222 or 2N3906 would work fine. When you choose, be sure to look for one that does not self resonate, i.e. make sound when connected to a power source. Most are able to take a variable frequency input.

[RyanN]

I've run into a bit of a problem today. I was testing the whole setup, so I left it running for about half an hour. Every thing seemed fine. I turned it off and went to go run some errands, and when I came home I found that it was on. So I pushed the power switch off and it stayed on. "Hmm...," I thought to my self so I disconnected the battery and it turned off. I reconnected it and left it off. I went to do some chores around my house, came back to my room and found it on again! Somehow, this thing keeps on turning itself on, and I'm not sure how it can do it with the way I have the power switch wired. I'm totally lost on to what is causing this because there is no way for it to happen with the setup I have. You can see that the power relay is connected to the fuse panel, which must receive power from the power switch first in order to even turn on. Here is a rough hand drawn schematic of my electrical circuits:
http://nazaretian.homeip.net:8000/ry...%201%20001.png

EDIT: Also it is receiving power from something non-mechanical. So I guess it's leaking through a transistor or something, but I don't see how since they're all connective negatively.