28119 Parallax Inc, 28119 Datasheet - Page 59

• Manufacturer Part Number: 28119
• Description: KIT UNDERSTANDING SIGNALS
• Manufacturer: Parallax Inc

Specifications of 28119

• Lead Free Status: Contains lead
• Accessory Type: Oscilloscope
• Interface Type: USB
• For Use With/related Products: BASIC Stamp® 2 and Board of Education
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

to charge for at least 10 ms (to 5 V) then disconnect the power supply, it will take 2 ms
for the capacitor to discharge to 37% or 1.85 V.
This use of capacitors and resistors allows you to use the BASIC Stamp to measure
resistance and capacitance. Because the time constant is always the same for an RC
network, we can measure the discharge time with the
threshold for BASIC Stamps is 1.4 V, meaning above 1.4 V the BASIC Stamp detects
logic 1 and below 1.4 V it detects logic 0. To measure the RC constant or time, set the
I/O pin high for several milliseconds allowing the capacitor to charge to 5 V. Then the
RCTIME
capacitor to discharge below 1.4 V.
Different resistor sizes affect the charge or discharge time. The signal on the bottom of
Figure 4-3 indicates when the I/O pin was set to an input, thereby making it high
impedance at Time = 0 seconds. At this point the capacitor starts to discharge through the
series resistor. The BASIC Stamp counts how long it takes the capacitor to fall to 1.4 V
in 2 µs increments.
Output
Voltage
(volts)
Input
Voltage
(Volts)
command will make the I/O pin an input and count the time it takes for the
5
4
3
2
1
0
-0.02
5
4
3
2
1
0
-0.02
-0.01
-0.01
0
0
V
1
0.01
0.01
V
2
V
0.02
0.02
3
V
V
V
V = 1.4 V
1
2
3
t
→
→
→
0.03
0.03
R = 10 k
R = 15 k
R = 5 k
2
3
1
Time, (Seconds)
0.04
0.04
Ω
Ω
Ω
RCTIME
V
t
0.05
0.05
command. The logic
Figure 4-3:
RC circuit responds
differently to three
different resistance
values.
Note how each
output takes a
different amount of
time to decay, or
discharge, from 5
Volts to 1.4 Volts.