Status Report - GREEN
1kHz clock
Introduction & Background
The LM555CN timer (aka 555 timer) is a chip that can be used in a variety of pulse, timer and oscillation devices. It is a very useful IC because its cheap price, abundance and many different configurations.This is the chip that will be used to provide the 1kHz clock used to drive the 7-segment display, running the decoder as well as the multiplexer.
To create the desired 1kHz square wave signal, the 555 timer will be configured in astable mode
The LM555CN timer (aka 555 timer) is a chip that can be used in a variety of pulse, timer and oscillation devices. It is a very useful IC because its cheap price, abundance and many different configurations.This is the chip that will be used to provide the 1kHz clock used to drive the 7-segment display, running the decoder as well as the multiplexer.
To create the desired 1kHz square wave signal, the 555 timer will be configured in astable mode
System description
Astable mode
In the configuration to the left, the 555 timer produces a square wave out of the output pin 3, which is represented by the sharp edge transitions between the lows and highs on the oscilloscope. Its called astable because of the constantly changing voltage level.
The frequency (f), period (T), duty cycle (%high) are controlled by R1, R2 and C1
Capacitors are used in this circuit to oscillate a DC power supply.
The oscillation cycle repeats as below:
-Capacitor begins to charge, but initially have low resistant, triggering a high output in the 555 timer.
-Capacitor builds up charge from Vcc (5V), gains resistance, and looses current, triggering a low signal in the 555 timer.
-Capacitor is discharged until it triggers to high output in the 555 time then repeats cycle
The formula, f = 1.44/((R1+R2)*C) is used to calculate the frequency.
Using the desired frequency, 1kHz and available parts from kit, 1kOhm resistor, 100kOhm potentiometer, 3 - 10nF capacitor and 47nF capacitor
-Let R1 = 1kOhm
-Let C = 3*10nF + 47nF
-R2 then equals to 17.7 kOhm
In the configuration to the left, the 555 timer produces a square wave out of the output pin 3, which is represented by the sharp edge transitions between the lows and highs on the oscilloscope. Its called astable because of the constantly changing voltage level.
The frequency (f), period (T), duty cycle (%high) are controlled by R1, R2 and C1
Capacitors are used in this circuit to oscillate a DC power supply.
The oscillation cycle repeats as below:
-Capacitor begins to charge, but initially have low resistant, triggering a high output in the 555 timer.
-Capacitor builds up charge from Vcc (5V), gains resistance, and looses current, triggering a low signal in the 555 timer.
-Capacitor is discharged until it triggers to high output in the 555 time then repeats cycle
The formula, f = 1.44/((R1+R2)*C) is used to calculate the frequency.
Using the desired frequency, 1kHz and available parts from kit, 1kOhm resistor, 100kOhm potentiometer, 3 - 10nF capacitor and 47nF capacitor
-Let R1 = 1kOhm
-Let C = 3*10nF + 47nF
-R2 then equals to 17.7 kOhm
A pin out diagram of the LM555 IC correspond the wiring
1. GND - Ground
2. TRIG - Trigger, timing interval starts when falls below 1/3 Vcc 3. OUT - Signal output 4. RESET - Resets the timing internet when grounded, active low 5. CTRL - Controls interval votlage divider 6. THR - Ends timing interval if high than CTRL 7. DIS - Open collector output 8. Vcc - Supply voltage |
Testing
Figure 1: 1kHz Clock schematic
Testing
Oscilloscope Channel 1
Plus terminal is connect to Pin 3 and minus terminal is connected to ground.
Oscilloscope Channel 2
Plus terminal is connect to the node between the threshold, trigger and the capacitor.
Result
The measured frequency on the oscilloscope is 1.4kHz.
Tuning
R2, the potentiometer is then adjusted until oscilloscope displays 1.0kHz.
The resultant resistance of R2 is 25kOhm therefore the effective capactance is 55nF
Oscilloscope Channel 1
Plus terminal is connect to Pin 3 and minus terminal is connected to ground.
Oscilloscope Channel 2
Plus terminal is connect to the node between the threshold, trigger and the capacitor.
Result
The measured frequency on the oscilloscope is 1.4kHz.
Tuning
R2, the potentiometer is then adjusted until oscilloscope displays 1.0kHz.
The resultant resistance of R2 is 25kOhm therefore the effective capactance is 55nF
Oscilloscope screen captures
Channel 1 displays the output waveform and measures its frequency.
Channel 2 displays the input waveform and measures its frequency.
Channel 2 displays the input waveform and measures its frequency.
Conclusion
The astable mode circuit with the corresponding component was able to produce as clock signal of 1.0kHz initially.
After a 24 hour trial period, the measured frequency of the output stayed consistently at 1.0kHz.
The astable mode circuit with the corresponding component was able to produce as clock signal of 1.0kHz initially.
After a 24 hour trial period, the measured frequency of the output stayed consistently at 1.0kHz.
Resources
LM555CN - Datasheet
100kOhm Potentiometer
1kOhm resistor
Ceramic Capacitors
Oscilloscope
Power Supply
Leads and connectors
FreeView Software
LM555CN - Datasheet
100kOhm Potentiometer
1kOhm resistor
Ceramic Capacitors
Oscilloscope
Power Supply
Leads and connectors
FreeView Software