Download Appendix F - Testing Results of Electrical Components

Appendix F
Results of Electrical AspectsTesting
As with any design, expected and actual operation of the final prototype may vary
quite substantially. To ensure that the final incontinence control device performed as
required, a series of tests were devised to measure the following:
Reliability of the Transfer of 12 Measures of Bladder Fullness
Reliability of the Current Consumption Calculations
Reliability of the Valve Control Signal
Reliability of the Valve Safety Feature
Reliability of the Wrist Module Push Button
Susceptibility of Wireless Communication to Interference
Distance Required for Proper Wireless Communication
Reliability of the Near to Full Bladder Safety Feature
Reliability of the Transfer of 12 Measures of Bladder Fullness
The ability of the watch LCD to properly display the bladder fullness when a
pressure sensor signal was applied was tested. For the incontinence control device, a 10
bit ADC was used to digitally convert the output of the pressure sensor. The resolution of
A/D converter was 3V / 210 = 0.003V. Twelve levels of bladder fullness were measured
as 12 increments of full circle on the watch LCD. Thus, each 1/12th section of the watch
LCD display circle would correspond to: 3 V/12 = 0.25V.
The following table indicates the ideal relationship between the pressure sensor
voltage and the number of segments (1/12th sections) that would be filled on the watch
LCD.
Pressure Sensor Voltage
No. of Segments Filled (1/12th Section)
0.003 – 0.250V
1
0.253 - 0.500V
2
0.503 – 0.750V
3
0.753 – 1.000V
4
1.003 – 1.250V
5
1.253 – 1.500V
6
1.503 – 1.750V
7
1.753 – 2.000V
8
2.003 – 2.250V
9
2.253 – 2.500V
10
2.503 – 2.750V
11
2.753 – 3.000V
Theoretically 12, but this level is never
displayed on the wrist watch LCD because
the valve is forced upon at this level.
In this test, a voltage regulator was used to generate different voltages that would
simulate the output from a pressure sensor. The voltage regulator was connected to the
analog input on the bladder module microcontroller, and the wrist module display and
general behavior were observed. The value of the voltage regulator was monitored using
a voltmeter with precision of up to 3 decimal places. The outcome is depicted by the
following step graph:
Figure 1: Voltage Response Step Graph
As this step graph shows, the results showed that the conversion of pressure
sensor voltage to watch LCD segment display was very precise and exactly complied
with the ideal results of the previous table. These results prove the proper function of the
ADC, wireless communications and LCD conversion. As for the 12th level, because it is
not displayed on the watch LCD, the valve open signal was used to measure this level
instead. A safety features of the incontinence control device automatically opens the
valve at the 12th level and thus the watch LCD never draws a full circle to indicate the
12th level.
The following pictures represent some of the stages of the testing. Note that the
voltmeter used was capable of indicating up to 2 significant digits. As a result, to check
the ranges of the voltages and their corresponding output level, the maximum and
minimum values tested within a level were within 0.01V of the actual values. This
tolerance ensured that missing information about the third digit did not bias the testing.
However, hen performing this test for the step graph, the value of the voltage regulator
was precisely measured with a voltmeter up to 3 decimal places.
Voltage range tested: 0.003- 0.250
Expected number of 1/12th segments: 1
Voltage range tested: 0.253 - 0.500
Expected number of 1/12th segments: 2
Voltage range tested: 1.253 - 1.500
Expected number of 1/12th segments: 6
Voltage range tested: 2.003 - 2.250
Expected number of 1/12th segments: 9
Voltage range tested: 2.253 - 2.500
Expected number of 1/12th segments: 10
Figure 2: Voltage Range and Watch LCD Testing
Reliability of the Current Consumption Calculations
Based on the theoretical calculations, the life expectancy was estimated at 40 days
for the bladder module and 33 days for the watch modules. To confirm that the minimum
threshold of 30 days was met for the bladder module, current consumption was
experimentally measured. The current consumption for the watch module was also
measured for completeness. An experimental setup for measuring the current usage is
shown below:
\Figure 3: Current Consumption Experimental Setup
The setup consisted of a resistor placed between the battery and components of
either the watch or bladder modules. These modules then performed specific tasks (such
as transmitting or receiving data, measuring pressure, etc). An oscilloscope then
measured the voltage drop across this resistor, and using V = I x R, the current
consumption was calculated. The oscilloscope was necessary to measure indirectly the
small currents. The current consumed by each component (such as the valve,
microcontroller and transceiver, watch LCD, etc) was recorded and used to estimate
actual life expectancy. The findings are shown in the table below:
Bladder Module
Action and Components
Microcontroller and transceiver (TI MSP430 and TI CC2500)
during regular receive and transmit mode
Valve (Lee Series 120) during an open/close cycle
along with MOSFET driver (MIC4426)
Pressure Sensor (Freescale MPX5010) upon regular pressure
sensing and ADC
Total Estimated Current Consumption
Estimated Life Expectancy
Watch Module
Action and Components
Microcontroller and transceiver (TI MSP430 and TI CC2500)
during regular receive and transmit mode
Watch LCD (Futara Zero-G) when displaying regular pressure
data along with three transistors (2N930)
Total Estimated Current Consumption
Estimated Life Expectancy
Average Current Consumption
5.6uA
0.37mA
8uA
0.3836mA
300mAh/0.3836mA
= 32 days
Average Current Consumption
5.1uA
0.36mA
0.3651mA
300mAh//0.3651mA
= 34 days
As these calculations show, the actual life expectancies for the bladder and watch
modules were close to the theoretical predictions. The bladder module would actually last only 32
days, although in theory it should last around 40 days. This discrepancy can be explained by
unaccounted for losses during actual operation. One such loss could be the fact that although the
bladder temperature would be around 37°C,
the ambient temperature during testing was
25°C. As the temperature increases, current losses decrease for many components, especially the
MOSFET driver. The watch module, by contrast, was predicted to last 34 days, which is one day
longer than theory predicted. This discrepancy of one day is very little, and supports the original
calculations.
Reliability of the Valve Control Signal
Another test was used to determine how reliable the valve control signal was.
Opening or closing the valve used in the design required pulses of at least 1ms in duration
and with an amplitude of 5V. A pulse of 1 ms and 5V needed to be reach Pin B of the
valve (while Pin A was grounded) for the valve to open. For closing, the process reversed
and the pulse needed to sent to Pin A. To ensure that the bladder module created the
proper signal for the to open and close the valve, the following test was devised.
To begin with, the system was reset to ensure that the first press of the wrist
module push button would open the valve and the second press would close the valve.
Oscilloscope pins from channel 1 and channel 2 were connected before the Valve Pin B
and Pin A RC circuits, respectively: These points are labeled as Point A and Point B in
the figure below.
Figure 4: Oscilloscope Measurement Circuit
The figure below shows the oscilloscope display after the watch module push
button was pressed for 5 s. As can be seen, a pulse of duration 1ms and amplitude 5V was
generated on channel 1 and a zero value on channel 2. These were the proper signals for
opening the valve.
Figure 5: Valve Opening Signal
The push button was repressed and held again fro another 5 s and the results of
figure x was observed. This time a pulse of 1 ms duration and 5V was observed on
channel 2, with channel 1 staying at zero. This indicated proper signals for closing the
valve.
Figure 6: Another Valve Opening Signal
Thus it was concluded that bladder module produced the proper signal to operate
the opening and closing of the valve.
Reliability of the Valve Safety Feature
A test was devised to measure the reliability of the safety feature used to monitor
the duration of the valve control pulse. The valve required a signal of minimum 1ms
duration to turn on. At the same time, the rated value for the duration of the pulse was 2 s.
In order to ensure that no pulse longer than 2 s was used, an RC filter was used in
conjunction with a MOSFET driver to ground the valve input voltage after the time
constant of the filter. The MOSFET driver triggered at 1.2 V, and once this threshold was
reached, the 3V input from the microcontroller would be cut down to 37% of its value
after the filters’ time constant expired. The values of R and C were chosen such that their
time constant was equal to 1.5 s. A 10mF capacitor and 147 Ohms resistor were used for
this purpose.
To observe and confirm the proper functioning of this safety mechanism, the
following procedure was implemented. A 3s pulse was intentionally coded to be
produced on Pin 3 of the EZ430-RF3500 target board. Next, the pulses created at Point C
and D, as shown in the circuit below, were displayed on the oscilloscope. Finally, the two
pulses were compared and analyzed.
Figure 7: Oscilloscope Measurement Circuit
The figures below show the pulses obtained at Point D and Point C on the
Oscilloscope:
Figure 8: Output at Point D
Figure 9: Output at Point C
Note that at nearly 1.5s, the 3V signal reached 37% of its value (1.11V). This
result matches the expected time constant. Also, at Point C, the pulse is cut off after 1.5s.
This finding proved that the pulses sent to the valve would last no be longer than 1.5s and
thus the valve safety feature functions as expected.
Reliability of the Wrist Module Push Button
The reliability of the push button located on the wrist module was tested to
determine the reliability of the valve open and close signal. To test this feature, the
duration and format of depressing the wrist module push button was determined. The
proper mechanism for opening or closing the valve required the push button be depressed
for at least 5s. After completing this action, if open, the valve will close and vice-versa.
This 5s delay was included as was part of a safety mechanism to avoid unwanted opening
of the valve if the button was hit by mistake.
To test the proper function of the push button, it was pressed for durations of 1, 2,
3, and 4 and 4.5 s. The results showed that in these cases, as expected, the valve was
unaffected. Upon pushing the button for 5s, the valve was activated.
In addition, the effect of depressing the push button for longer than 5s was also
tested. A continued press of the button over 5 s was performed for 8, 10 and 15 s. It was
observed that such actions resulted in a single state change of the valve (only one pulse
was observed on the valve pins). These results agree with the fact that the external
interrupt would be triggered only once upon observing a rising edge. Thus, multiple valve
open or close actions would not occur. By contrast, if a polling scheme was used in the
program for retrieving the push button signal, a continued press of the button would have
caused the multiple opening and closing of the valve while button was being depressed.
As a final test, a series of pulses with 1 second, 2 second, 3 second and 4 second
periods were generated by pressing and releasing the button at specified time intervals.
This test attempted to ensure that such pulses did not accumulate and that no cascading
effect would be observed. As expected, no action (either to open or close the valve) was
triggered upon such frequency of pulses. This result was due to the fact that the
mechanism for triggering any action began at the received rising edge and measured the
5s time duration from that the time until the next falling edge.
As a final conclusion, these valve push button tests indicated that the 5s duration
safety feature of the valve control signal was rigorously implemented.
Susceptibility of Wireless Communication to Interference
A test was devised check the susceptibility of the wireless communication to the
presence of other transceivers. In this test, two extra transceivers (an extra AP and ED)
were brought into close contact (within a few meters) with the regular bladder and wrist
module transceivers.
For the first test, the extra transceivers were turned on, and following that, the
bladder and wrist module transceivers were turned on. The effect of having the extra
transceivers on before the module transceivers was observed. The results showed that the
module transceivers were able to link properly using their fixed flash addresses, and thus
ignore the extra devices present.
For the second test, the module transceivers were turned on, and following that,
the extra transceivers were turned on. The effect of this test on functioning of the bladder
and wrist modules was observed. Once again, the results showed that the module
transceivers continued to function properly regardless of the presence of the extra
transceivers.
In both tests, since the linking process of the SimpliciTI protocol (as described in
the Wireless Communication section) required a specific address to complete a link, the
module transceivers could only link to each other. Thus, these test results indicated that
the system was reliable even in the presence of multiple transceivers (within a few
meters) and was sufficiently robust against interference.
Distance Required for Proper Wireless Communication
A test was devised to learn more about the distances within which the module
transceivers were able to maintain proper communication. In this test, the distance
between the bladder and wrist module transceivers was varied. It was then observed if the
watch LCD displayed the bladder fullness correctly and if the valve control signal
functioned properly. Distances ranging from 2cm to 30m were tested, and these distances
are well within the range of normal operation. The result of this testing is presented in the
table below:
Distance
Communication Reliability
2cm
Reliable
10cm
Reliable
1m
Reliable
20m
Reliable
25m
Reliable
30m
Unreliable
As these results show, the system had the ability of maintaining proper
communication for a large distances of up to 25m. However, if the bladder and wrist
transceivers were separated by a distance of more than 30 m, the connection was
unreliable. It is important to note though that the bladder and wrist modules, in proper
operation, would never exceed separations of more than 2m because of the dimensions of
the human body. Thus, these results are perfectly acceptable and prove that the wireless
communication distance is within an acceptable range.
Reliability of the Near to Full Bladder Safety Feature
The code implemented includes a safety feature that prevents the bladder from
becoming completely full, causing the valve to automatically open regardless of user
input. Testing of the reliability of this feature was done. In terms of the watch LCD, at the
11th segment (out of 12 segments), the user was alerted of the bladder fullness with a
blinking of the display (a blinking taking the form of a redrawing of the current section of
the circle). It was hoped that the user would empty the bladder upon receiving this signal.
However, if the bladder entered the 12th segment of the watch LCD, the code
implemented inside the bladder module would automatically run the subroutine in charge
of opening the valve. This attribute was included as a safety mechanism for the bladder to
be emptied before any internal damage could be done to the bladder wall or the implanted
circuit because of high pressures.
To ensure that the expected operation successfully took place, the following tests
were done: The analog input voltage from a voltage regulator was increased to 2.51V
(equivalent to the 11th segment of the watch LCD). The expected visual alert was
observed in the form of the blinking of the current display being redrawn in short
intervals. The voltage was then increased to 2.8V (equivalent to the 12th segment) and it
was observed that the display halted and the oscilloscope indicated a 1 ms pulse.
At this point, the voltage was decreased to 0.2 V (equivalent to the 1st segment of
the watch LCD) in order to observe proper operation of the watch after handling the
critical situation. It was observed that the watch resumed its operation by resetting and
later filling in 1/12th of the circle. The watch module push button needed to be depressed
again to close the valve, and this closure was observed by seeing a 1 ms pulse on the
oscilloscope.
The above test was repeated again, only this time the voltage was first set to 2.3V
(equivalent to the 10th segment of the watch LCD). The voltage was then increased to 2.8
V (equivalent to 12th segment) quickly, by passing the 11th level. . It was observed that
the watch LCD halted its display and displayed the alert mechanism. A pulse of 1ms at
the input to the valve was observed shortly after on the oscilloscope. Upon decreasing the
voltage to 0.2V, the watch resumed its operation by resetting and indicating the
equivalent 1/12th of the circle. The aim of this procedure was to test the ability of the
device to enter the critical stage from any voltage ranges and any previous levels
Another test was applied to see what would happen if the user attempted to close the
valve after it had automatically opened (when the bladder was full). In order to test this condition,
the pressure sensor simulated voltage was set to 2.8V (equivalent to the 12th segment of the watch
LCD) and the valve open signal was observed on the oscilloscope. At this point, the push button
was depressed to attempt to close the valve before the bladder had emptied. The results showed
that the watch LCD still displayed the 12th segment and no pulse indicating the closer of the valve
was observed. In a parallel test, the voltage was decreased to 2.6V (equivalent to the 11th segment
of the watch LCD) and the button was pressed again. This time, the close valve signal was
produced and the 1ms signal was observed on the oscilloscope. This test also confirmed the
functionality of the program. According to this test and the program, the would be forced open at
all times during the 12th level. In real life situation, the valve would open and allow urine to
discharge. Only after enough urine had discharged to downgrade the watch LCD from the 12th
segment of the Watch LCD did the user have the option of closing the valve again.
The above two tests indicated that the valve was forced open whenever bladder reached
the critical stage of being full. The valve would stay open until the bladder was no longer in the
critical condition.