Version 1.6 - May 28, 2012
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over temperature, over current and over and under voltage conditions. As mentioned above
the two half-bridge chips may be connected either as an H-bridge or as two independent half-
bridges. This flexibility makes the MegaMoto suitable for driving a wide variety of DC loads.
The MegaMoto features a current sense output from each half-bridge power chip. This output
is a voltage proportional to the current flowing through the chip. The voltage output is
approximately 0.075V per Ampere of current. When jumpered for individual current readings
the CA and CB outputs reflect the current passing through the M1 and M2 motor terminals
respectively. When jumpered for combined current output the CA output reflects the
combined current flowing through both power chips. However, the current reading may not be
negative so in an H-bridge configuration only the one power chip passing current in the
positive direction (
high-side switch on
) will present an output; the other chip presents no
voltage output. So in combined current mode the current output is correctly proportional to the
current passing through the H-bridge.
5. Additional notes on driving the MegaMoto
The MegaMoto is designed to be stacked up with several units being controlled by a single
Arduino base. A number of aspects of the MegaMoto circuit are important but may not be
obvious to the new user.
Enable
: The unit must have a logic high signal on the enable input to allow the power chips to
function. Unlike some of the other power drive chips available the Enable input cannot be
pulsed with a PWM signal. The various internal protection circuits require a steady Enable
state to function properly. Thus at least one jumper should be placed on the Enable jumper
block for each MegaMoto even if there are several units stacked. Each unit’s inputs are
indpendent.
The MegaMoto requires an Enable signal a simple 5V connected to the input via the available
jumper block will function properly. However, in that case the unit cannot be disabled.
Further if the unit ever goes into thermal or over current shutdown the Enable input cannot be
used to reset the chip and the entire Arduino system power must be cycled. Connecting the
Enable to 5V is recommended only when the load is very unlikely to encounter an overload or
when an overload should never automatically reset i.e. user action is required before
resuming operation.
If several MegaMoto units are stacked onto an Arduino base it is possible to use a single
digital pin to enable/disable all of the MegaMotos. This does not allow individual
enable/disable functions but can be used if all the loads (motors) are always enabled or
disabled together. For example a kinetic sculpture might use three motors but would never
operate just a single motor alone.
PWM Source:
As with the Enable input above, each MegaMoto power chip must have a
PWM source connected to function.
If no PWM source is connected the power chip will
connect its output to the Batt + rail.
This is important to keep in mind during system-reset
conditions on the Arduino. When doing program load and other extended reset conditions
half-bridge connected motors will run. H-bridge connected motors will not spin because both
A-side and B-side outputs will be at the same level. Battery power should be removed during
program development. It is not necessary to have battery connected when the system starts
up. It may be connected at any time and disconnected at any time without interrupting the
Arduino program.
The PWM inputs do not have to be pulsed. A steady on-off switch-like action of the output
can be achieved if desired. Thus D3, for example, might be used as a simple digital output