ELM412
Elm Electronics Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
Connection Diagram
PDIP and SOIC
(top view)
V
DD
V
SS
1
2
3
4
8
7
6
5
Piezo Element Driver
The ELM412 is an 8 pin oscillator circuit for
driving piezo-electric elements. With the exception of
one external resistor, all of the circuitry required to
drive a typical piezo `bender' is contained within this
chip.
This circuit allows the user to select one of eight
possible operating frequencies by way of three logic
level inputs. These eight frequencies represent
some of the more common resonant frequencies
used for piezo elements. If desired, the frequency
can be continually varied by the controlling circuit.
The output of the ELM412 uses a bridge
configuration to obtain maximum audio drive for a
given power supply level. A single input pin is all that
is required to gate the output on and off.
Typically the ELM412 is used to relieve a
processor of the duty of waveform generation,
allowing it to concentrate on other activities,
although the circuit can also be used in stand-alone
tone generator circuits.
F2
F1
Description
Computer controlled tone generation
Alarm warning signals
Keyboard click generation
Logic probe circuits
Applications
Block Diagram
1 of 4
Low power CMOS design
Wide supply range - 3.0 to 5.5 volt operation
No external timing elements required
Generates eight common piezo frequencies
Bridged output for greater audio power
Modified waveform for reduced harmonics
Features
ELM412DSB
Out1
Enable
F0
Out2
2
3
F2
F1
Out2
Programmable
Oscillator
Waveform
Generator
7
6
F0
Out1
4
Enable
5
F2
F1
F0
Frequency
L
L
L
600
L
L
H
1200
L
H
L
2000
L
H
H
2400
H
L
L
2800
H
L
H
3200
H
H
L
3600
H
H
H
4000
Table 1
ELM412
Elm Electronics Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
Pin Descriptions
Ordering Information
These integrated circuits are available in either the 300 mil plastic DIP format, or in the 200 mil SOIC surface
mount type of package. To order, add the appropriate suffix to the part number:
300 mil Plastic DIP............................... ELM412P
200 mil SOIC..................................... ELM412SM
2 of 4
Absolute Maximum Ratings
Storage Temperature....................... -65C to +150C
Ambient Temperature with
Power Applied....................................-40C to +85C
Voltage on V
DD
with respect to V
SS
............ 0 to +7.5V
Voltage on any other pin with
respect to V
SS
........................... -0.6V to (V
DD
+ 0.6V)
Note:
Stresses beyond those listed here will likely damage
the device. These values are given as a design
guideline only. The ability to operate to these levels
is neither inferred nor recommended.
All rights reserved. Copyright 1999 Elm Electronics.
Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be
given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information
described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these
products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or
systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve
reliability, function, or design.
V
DD
(pin 1)
This pin is the positive supply pin, and should
always be the most positive point in the circuit.
Internal circuitry connected to this pin is used to
provide power on reset of the microprocessor, so
an external reset signal is not required. Refer to
the Electrical Characteristics section for further
information.
F2 (pin 2), F1 (pin 3) and F0 (pin 4)
These are the frequency select inputs. One of
eight frequencies are selected according to the
logic levels on these pins, as shown in Table 1.
Enable (pin 5)
This schmitt trigger input pin is used to control
the output. A high level at this input will allow the
outputs to appear at pins 6 and 7, while a low
level inhibits the output. The schmitt trigger input
is convenient for interfacing to slowly changing
signals, as from an RC coupled circuit.
Out2 (pin 6) and Out1 (pin 7)
These complementary outputs are used to drive
the piezo-electric element through a current
limiting resistor. The outputs switch between Vdd
and Vss with a combined duty cycle of
approximately 67% (see Figure 2). This results
in reduced harmonics in the output signal and
more energy to the fundamental. The output
always consists of complete cycles, as the cycle
that is in progress when the enable input goes
low will always be allowed to complete.
V
SS
(pin 8)
Circuit common is connected to this pin. This is
the most negative point in the circuit.
ELM412DSB
Elm Electronics Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
ELM412
Electrical Characteristics
3 of 4
All values are for operation at 25C and a 5V supply, unless otherwise noted. For further information, refer to note 1 below.
Characteristic
Minimum
Typical
Maximum
Conditions
Units
Supply Voltage, V
DD
3.0
5.0
5.5
V
V
DD
rate of rise
0.05
V/ms
Average Supply Current, I
DD
0.60
2.4
mA
Notes:
1. This integrated circuit is produced with a Microchip Technology Inc.'s PIC12C5XX as the core embedded
microcontroller. For further device specifications, and possibly clarification of those given, please refer to the
appropriate Microchip documentation.
2. This spec must be met in order to ensure that a correct power on reset occurs. It is quite easily achieved
using most common types of supplies, but may be violated if one uses a slowly varying supply voltage, as
may be obtained through direct connection to solar cells, or some charge pump circuits.
3. Internal IC current only. Does not include any piezo or other currents.
4. A series resistor must be used to limit the current peaks due to the relatively large capacitance (~50nF) of a
piezo element. Maximum size is determined by the desired volume level.
5. Frequency error is both supply and temperature dependent, typically as shown in Figure 1 below.
Input low voltage
V
SS
0.15 V
DD
V
Input high voltage
V
DD
V
0.85 V
DD
Output low voltage
0.6
V
Output high voltage
V
V
DD
- 0.7
Current (sink) = 8.7mA
Current (source) = 5.4mA
see note 2
ELM412DSB
Output Duty Cycle
%
67
1.0
2.4
mA
V
DD
= 5V, see note 3
V
DD
= 3V, see note 3
see note 4
Output series resistance
2200
470
Figure 1. Average Frequency Error
see note 5
Frequency Accuracy
%
2
-40
0
40
80
Temperature (C)
0
-6
+6
% Error
-4
-2
+4
+2
V
DD
= 5V
V
DD
= 3V
slow
fast
Elm Electronics Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
Example Application
ELM412
Output Waveforms
4 of 4
ELM412DSB
Operation of the ELM412 is straightforward,
requiring little explanation. Typically the resonant
frequency of the piezo element is determined, and
pins 2, 3 and 4 are connected for this frequency. In
the circuit of Figure 3, the frequency has been set for
2400Hz. A single bit from a control circuit is then
used to turn the buzzer on and off.
The 2.2K
resistor shown in the circuit serves
two purposes. One is to provide a current limit for the
ELM412 as it tries to rapidly change the piezo
voltage (the piezo is like a large capacitor), and the
other is to simply limit the output loudness.
The only other detail in Figure 3 is the customary
0.01F capacitor for supply decoupling. It's always
good practice to add one, although it's often not
essential.
Control Bit from the
Microprocessor
(1=on, 0=off)
0.01F
+5V
1
2
3
4
8
7
6
5
Piezo
Element
2.2K
Figure 3.
Out1
Enable
Out2
Out1 - Out2
The output waveforms are generated as long as
the enable input remains high. When brought low,
the current cycle completes before the output
ceases.
Figure 2.
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