Watt Meter

Project reference: http://homepages.paradise.net.nz/bhabbott/wattmeter.html

ASM code: http://homepages.paradise.net.nz/bhabbott/watt/wattmeter.asm

Schematic: http://homepages.paradise.net.nz/bhabbott/watt/Wattmeter.gif

My Watt meter:
I am using the schematic as shown above, however there is minor change where I didn’t use any switches (S1, S2, and S3) and the shunt resistor, R15 used is 1 Ω. I’d asked the author of this project, he mentioned I can neglect the rpm input at RB0 pin 6 of PIC16F88. So basically the overall idea is to measure the power dissipated in terms of watt.

After the schematic has been connected, I manage to get this on the LCD screen:

*However, sometimes I may have readings even without connecting any load to it.
Question 1: May I know what cause this?

Then, I tried to connect both the LOAD + and LOAD – together, what I get is:

The maximum value allowed by the author and the project.

All values are constant while the Ah value keeps on increasing. (I think it is because I want to measure watt, so timer is needed here).

There are several questions that I really need to know regarding this project as I am an ASM language numb. I really appreciate your help on this.

1. May I know the overall concept on how this watt meter is built? As I know to get Watt (power), I need to know voltage, current, and resistance. In this project, there are two parts, one on the shunt current (if not mistaken), and the one connected to the PIC16F88 measuring the voltages. So computation on the reading (watt) is done by getting the analog values of both and do the analog to digital (ADC) within the PIC.
2. I see there are changes when load is connecting to the watt meter. Only the voltage reading 25.58V keeps constant on the LCD while other changing. Ah (Ampere hour) is increasing secondly and both the watt (W) and current (A) have the values changes. May I know is the watt and ampere value are being shown simultaneously each time the calculation done instantaneously?

3. Refer to the connection as shown above; there are 4 outputs from the PIC to the LCD. RA4 to DB7, RB1 to DB6, RB2 to DB5, RB3 to DB4. As this watt meter using a 16x2 line LCD, so as I know 2 data buses are corresponding to the characters displayed on the LCD and the other two are used to control the LCD. May I know which two data buses responsible for this? I need these two data buses to connect to the digital IO of my RF module.
4. I am using a 9V battery as the input. Providing the facts of using shunt resistor of 1Ω, I wonder what the range of the load I might use. And I found that for the four data buses, DB7 is the only one with high voltage of 3.8V. May I know what does that mean? Leak?


Well, I had gone through the progress of implementing the hardware until now. So hopefully I can have someone guide me and advice me on my debug progress. I really appreciate your help. Thank You. By the mean time I will also trouble shoot it on my own. Guidance and help are needed. Thanks again.

 

You cannot use these lines for getting the data. If you need a serial out you need to modify the code and using a spare pic pin to tx serially the content of the variables Volts; Current and Power

Well, this is the nightmare to me. As I am numb at ASM. So if serial is being used, means there will be only one output to my RF module isn't it? Because I am not sure what the 4 IO for ... s until now i cant make my decision on making the interfacing to my RF module.
Can any ASM programmer guide me?

 

Can you post the type of RF module you want to use?.

Almost all RF module (Xbee for example) use serial communication protocol.

Alberto

Oh ya, it is versatile ....
it has one serial input ....
and 7 digital IO..
for digital IO, no further modification needed ..
As for me, i will need to know which data buses involved in sending the values.

for serial, uart routine needed.

 

I am getting this when i emailed the author months ago...i wonder what does it means:

 

Well.... it is OK. Thanks for the reply.
Which means using programming, i can set RB0 as a single Digital output from the PIC?

Any assembly master here?

 

I just figured out that ..... for the meter, when I use my finger to touch on the LOAD + and step on the floor .. there is data transmitting over the RF module but no reading at the meter .. strange... what phenomena is that pls?

 

From the asm source code, there are calculations on the watt and ampere hour.
But for my project, i intended to get only the ampere hour reading out. So I tried my best to study the asm code though i am numb in asm.

Calculating the ampere hour

calc_Ah:
    add1632    Amps,AmpSum    ; AmpSum = accumulated Amps
    mov32    AmpSum,dd
    movi16    3600*3,aa    ; 3 reads per second, 3600 seconds per hour
    call    Div32        ; AmpHours = AmpSum  / (reads per hour)
store_Ah:
    mov16    dd+2,AmpHours

And here is the part to display the reading at a 16x2 line LCD

.....
call    Show_AmpHours     ; "9999.9W 99.99Ah"
.....

But the code is intended to display it on the LCD. How to modify it so that i can directly get a single stream for only the ampere hour data out from a PIC?