Manual OC32/NG
VPEB
Control your Miniature World
Page 32 of 48
Version 1.0 – December 15
th
, 2017
2017 Leon van Perlo
Each output can provide 500mA but
Take Care: the maximum total current for the 8 outputs of each group is 1 A.
There is not a real current limitation in the OC32. You have to take care of that yourself or
to be certain you have to put a fuse in between. So it is not possible to load all 8 outputs of
a single group with 350mA each. In the case of more "heavy" loads they have to be spread
over more groups.
6.1.3
Sink and Source Drivers (TB TBD62783)
If both a Source Driver and a Sink Driver are placed in one Group, two consecutive outputs
of that group are going to act as a pair. For the electronic engineers: this means that the
group is acting as an quadruple H-bridge. In most cases the load is connected between two
consecutive outputs. Those two consecutive outputs can have three different states:
•
Both outputs off = load off
•
Output Q+0 negative, output Q+1 positive = current into one direction.
•
Output Q+0 positive, output Q+1 negative = current into the other direction.
•
Both outputs on =
NOT ALLOWED
If you hook-up a DC motor, with this type of connection, not only the speed can be
controlled, but aso the directon of rotation. An application in practice would be a turnout
motor like Tortoise or Hoffman.
Attention: In this configuration only one output of each pair may be active
simultaneously! Otherwise the result is a shortcut and a fried driver IC. The OC32 has a
safety mechanism for this. To be sure that this mechanism works properly the "hardware
configuration" has to be set correctly (see OC32 firmware manual)
6.1.4
Resistor Array (5V outputs)
In this case a resistor network is inserted in the receptacle of the
Sink Driver
. A resistor
array is nothing else than multiple resistors in an IC housing. It fits into the place where a
driver would be placed otherwise.
A resistor array is not a real driver. The I/O Pin of the OC32 processor is connected through
a resistor to the equivalent I/O Pin of the module. The resistor provides some protection to
the processor and current limitation to protect the load. Because the processor operates
with 5V internally, the output voltage of this kind of output is restricted to 5V. The
electrical power is obtained from the processor directly. As a result the power is limited.
This setup can be used in the following situations:
•
Driving a servomotor. A servomotor has its own power supply and needs only a digital
control signal to determine the position. Sink and Source drivers would disturb the
control signal and for that reason the resistor array is used.
•
Driving a LED. The substantial advantage is that the series resistor for the LED is
incorporated in the OC32. The LED can be connected directly. Most often the LED is
connected between output and GND but it can be done between two outputs or
b5V and the output as well.
•
For using the I/O Pin as input. The input signal applied to the Pin shall remain between 0V
and 5V. The resistor acts as a (limited) security mechanism, so the input is not
immediately destroyed when accidently a wrong Voltage is applied to the Pin. When you
use all Pins of the bank as input, you best use a somewhat higher resistance value (e.g.
1k
Ω
) for improved protection.
•
More complex situations like 3 LEDs on the barrier of an automatic railroad crossing
(AHOB) which are driven with two outputs and two wires.
Control your Miniature World
VPEB
Manual OC32/NG
2017 Leon van Perlo
Version 1.0 – December 15
th
, 2017
Page 17 of 48
If you need the 5V interface, it can be made available
by a simple modification:
•
If not already present, solder a dual-pin header
(pitch 2,54mm) onto position JP3
•
Place a jumper on JP3 to activate the 5V
interface.
If you want to provide your own 5V supply, then
connect its minus to pin 2 of K1 (GND) and its plus
to pin 3 of K1 (5V).
Furthermore the following requirements need to be satisfied:
•
JP1 and JP2
may NOT
be installed.
•
The pin PWR on K1
may NOT
be connected.
•
Ideally the power voltage should be between 5.0V and 5.1V and be stabilized very well at
a short distance of the OC32. An improperly stabilized power supply or a long wire
length will lead to instability of the OC32. A negative voltage or a voltage higher than
5.5V will inevitably lead to a serious defect in your OC32 and costly repair!
4.6
Use of model railroad- and other transformers
4.6.1
Use of a locomotive transformer
If you have a locomotive transformer for a
DC system
, you can use it as a power source for
your OC32 and connected items. Take into account that in most cases a locomotive
transformer does not provide a real DC voltage, but a pulsing voltage.
For a correct operation it is highly advisable and in most cases even mandatory to smooth
the voltage pulses with a capacitor. This can be done by connecting the capacitor to the
supply voltage in parallel, preferably as close to the transformer as possible. The value of the
capacitor depends on the total current that you will need from the supply. As a guideline,
use about 2500
µ
F per Ampere. Obviously the specified voltage of the capacitor needs to be
higher than the voltage you will actually provide to the OC32.
Furthermore it is very advisable to mechanically block the direction switch on your
transformer, to prevent an accidental reversal of polarity from happening!
4.6.2
Rectification and smoothing of an AC voltage
If you don’t have a DC voltage but an AC voltage only, then you can transform that into a DC
voltage with 3 simple components. How this is achieved can be found in figure 9.
Attention: Since the rectified voltage will be connected to your OC32(‘s), the OC32(‘s)
will be connected to your digital system or to your PC and in the latter case your PC to
your digital system, it is essential that the AC voltage source (the transformer itself) is
not connected in any other way to your digital system. It might be feasible, but you have
to know exactly what you are doing, and how your digital system is constructed. If you
don’t know that, then see to it that the secondary side of the transformer (the low
voltage side) is not connected in any other way. Ignoring this warning can result in
damage of your OC32, your digital system or both!
So, if you have a separate AC transformer or a transformer with a separate secondary side
that you can use, you can use the schematics as shown in figure 9 for rectification and
smoothing. To the left you connect the output of your AC transformer. The value of the
capacitor depends on the total current you need. As a guideline, use about 2500
µ
F per
Ampere. The diode bridge needs to be able to cope with at least the voltage and current
that you are going to obtain and the voltage that the capacitor needs to cope with has to
Before mod Fig 8 After mod
