Transcript Frequency to Voltage Converter Used as RPM Gage

Frequency to Voltage
Converter Used as RPM Gage
Justin Dasah
David Hunter
Ellia Lim
Introduction
-In the robotics field there is a need to control
vehicles using small internal combustion engines.
-The drawback of small internal combustion engines
is that they come with very few sensors.
-In order to properly control the engine the
microcontroller must monitor various things such as
coolant temperature, oil pressure, and engine RPM.
• Oil pressure and coolant temperature
sensors are easy to read, and can be
connected directly to the microcontroller
since they are low voltage, low current,
and relatively clean.
• RPM however is a more difficult problem
since it must be read from the engine coil.
The Problem
• The problem with this is that the coil voltage is
large, and the output is extremely noisy which
may damage expensive components.
• Theoretically, the standard circuit that is
implemented in an RPM gauge will work.
However, in practice the noise and voltage
spikes coming from the engine coil will cause
damage to the circuitry and will also give
inaccurate voltage readings.
•Standard circuit implemented in an RPM gauge
-Output from the engine coil of a standard 6 cylinder engine
- As can be seen we have a noisy waveform, resembling a
square wave, with a large voltage spike reaching as high as
315V. This would surely damage any microcontroller.
The Solution
• In order to eliminate the large voltage spike of
315V, we installed a TVS diode (Transient
Voltage Suppression diode) in parallel with the
input.
• We also used an operational amplifier as a
comparator, to clean up the signal and generate
a useable square wave between 0 and 12 Volts
TVS Diodes
• A TVS diode is a gadget that protects
electronic devices from over voltages.
• The device works by drawing away
excessive current when the induced
voltage exceeds the zener breakdown
potential.
TVS Diodes
• It is represented by two opposing Zener
diodes connected in parallel with the circuit to
be protected.
TVS Diodes
• TVS diodes are preferred to other voltage
spike protection devices (such as varistors
or gas discharge tubes) due to their rapid
response time.
• This characteristic makes TVS diodes
useful for protection against massive
voltage spikes created by such things as
motor arcing.
TVS Diodes
• The TVS diode that we chose was the
World Products 1.5KE30A.
• This diode suppresses any voltage greater
than 41.4V
• This was chosen to discard the large
voltage spike without cutting of the
remainder of the signal.
TVS Diodes
• TVS Diodes are used to protect computer and
data processor circuits, power supplies, airframe
avionics and controls, telecom circuits, and
many other applications.
• These devices are designed to protect against
transient voltages generated by lightning,
electro-static discharge (ESD), and inductive
switching.
TVS Diodes
1.5KE30A
Op-Amp Comparator
• A comparator is a device that compares
two voltages or currents and switches its
output to indicate which is larger.
Op-Amp Comparator Circuit
Non-Inverting Terminal Input
Final Circuit
Results
1 Hz = 60 RPM
Frequency (Hz)
RPM
Voltage (V)
70
4200
6.20
65
3900
6.06
60
3600
5.65
55
3300
5.20
50
3000
4.72
45
2700
4.26
40
2400
3.80
35
2100
3.38
30
1800
2.99
25
1500
2.54
20
1200
2.07
15
900
1.61
10
600
1.16
5
300
0.85
0
0
0
Results
Voltage vs. RPM
7
6
6
5
5
Voltage (V)
Voltage (V)
Frequency vs. Voltage
7
4
3
4
3
2
2
1
1
0
0
10
20
30
40
Frequency (Hz)
50
60
70
0
0
500
1000
1500
2000
2500
RPM
3000
3500
4000
4500
Real World Applications
• Include turbines/wind turbines
• There are already frequency-to-voltage
converters in vehicle-monitoring
applications that evaluate the response
times of anti-lock braking systems
• Control of robotic vehicles
Future Improvements
• Include more filtering before operation
amplifier stage.
• Use Schmitt trigger instead of comparator.
• Design to operate at larger frequencies
Thank You