Pulse width modulated weighing platform

• US 6,313,415 B1
• Filed: 12/30/1999
• Issued: 11/06/2001
• Est. Priority Date: 12/30/1999
• Status: Expired due to Fees

• Current Assignee: Pitney Bowes Incorporated (Böwe Systec AG)
• Original Assignee: Pitney Bowes Incorporated (Böwe Systec AG)
• Inventors: Miller, Kenneth G., Maher, James P., Bass, Edward R.
• Primary Examiner(s): Gibson, Randy W.
• Application Number:
  US09/475,357
• Time in Patent Office: 677 Days
• Field of Search: 177/210.R, 177/210.FP, 177/25.13
• US Class Current: 177/25.13
• CPC Class Codes: G01G 23/3707 using a microprocessor

Abstract

An electronic scale uses an analog signal from a load cell which is converted directly to a pulse width modulated output signal. This pulse width modulated output signal represents the weight of an object on the scale and is sufficient to be directly read by a typical microcontroller. Therefore, no amplifier or analog to digital converter is required. The microcontroller then converts a signal representing the weight of the object on the scale to a weight value. A method of using the counter/timers on the microcontroller with synchronized overflow, is disclosed to enable a high resolution value of the pulse width modulated signal, which is then converted into a weight value for object'"'"'s weight given that the pulse width modulated output signal is proportional to the weight of an object placed on the load cell.

Claims

1. An electronic scale for weighing an object placed thereon, the electronic scale comprising:

(a) a load cell with terminals for providing an output voltage proportional to the weight of the object placed on the load cell;

(b) a pulse width modulated signal generator responsive to the output voltage from the load cell so as to generate a pulse width modulated output signal responsive to said output voltage; and

(c) a microcontroller responsive to the pulse width modulated output signal generated by the pulse generator so as to generate a weight data having a value proportional to the duty cycle of the pulse width modulated output signal wherein, the microcontroller includes programmable timer/counter arrays (PCAs) to time the pulse width modulated output signal used by the microcontroller to generate the weight data and a memory for the storage of a number of count overflows, wherein the microcontroller includes a first high resolution timer/counter and a second timer/counter, the first timer/counter is clocked to count at a faster rate than the second timer/counter, wherein the second timer/counter is preset with a predetermined count value so that it overflows at the same count value as the first timer/counter, wherein the number of overflows of the second timer/counter are stored in said memory.

2. A scale as defined in claim 1 wherein the first and second timer/counters are stopped and the values saved upon a transition of the pulse width modulated output signal.

3. The scale of claim 2 wherein:

(a) the microcontroller is an Intel®

8XC51FX based microcontroller.

4. A method for determining the weight of an article placed on a load cell comprising the steps of:

(a) placing an article on the load cell to generate an analog signal from the load cell which is proportional to a weight of the article;

(b) sending the analog signal to a pulse width modulated signal generator which directly converts the analog signal to a pulse width modulated signal which is readable by a microcontroller, said pulse width modulated signal having a duty cycle proportional to the analog signal, said pulse width modulated signal generated without amplification or use of an analog to digital converter;

(c) wherein the pulse width modulated signal contains rising edges and falling edges which form a duty cycle proportional to the weight of the article placed on the load cell;

(d) sending the pulse width modulated signal to a Programmable Counter Array (PCA) capture module of a microcontroller to enable a first timer/counter and a second timer/counter in the microcontroller;

(e) setting the first timer/counter and the second timer/counter to operate at different rates wherein the first timer/counter operates at a rate which is faster and has higher resolution than the second timer/counter;

(f) presetting the second timer/counter to a specific value such that it experiences overflow at the same time that the first timer/counter experiences overflow in a synchronized manner;

(g) starting the time/counters upon detection of a rising edge or a falling edge by the Programmable Counter Array (PCA) capture module;

(h) interrupting upon overflow of the second timer/counter, incrementing an overflow count value of the second timer/counter in a memory, logically adding a synchronization value to the second timer to enable the second timer to remain synchronized with the first timer;

(i) interrupting upon detection of a subsequent rising edge or a subsequent falling edge by the Programmable Counter Array (PCA) capture module;

(j) combining the overflow count value of the second timer/counter with the value from the first timer/counter to form a high resolution value representing the width of the High or Low portion of the pulse width modulated signal; and

(k) converting the high resolution value in the microcontroller to a weight value for the article placed on the load cell.

5. The method of claim 4 wherein the microcontroller operates at a predetermined frequency of oscillation (Fosc) wherein:

(a) the second timer/counter operates at the rate of Fosc divided by 4 (Fosc/4), and

(b) the first timer/counter operates at the rate of Fosc divided by 2 (Fosc/2).