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Ticker 16-8 => Booster version
Text ticker with 16*8 LEDs and an ATtiny- or an ATmega-Controller
The advantage that the 4094s drive low-current-LEDs directly and without
a current-limiting resistor is a disadvantage, if your LEDs consume 20
or more mA. That is the case if you plan a large display with 10mm LEDs.
It doesn't help to operate the 4094 at 15 or 18V operating voltage,
because the 4094 would die the heat death if you switch eight LEDs of
a column at once.
It is time for a boosted version, which extends the base schematic with
a high-LED-urrent booster. And for an intelligent power supply that can
deliver up to 128 x 20mA = 2.56A.
5.1 Design for a large display with 10mm-LEDs
This here would be a design for a 57.6-by-30 cm sized front display
with 10mm LEDs. The front is splitted into three parts, to be able to drill
the LED holes in the middle more conveniently. The two outer parts have
five LED columns each, the middle part six. The distance between the center
of the LEDs is 36 mm in horizontal and vertical direction.
This is the drill template for the middle section, which can also be used
for the two outer sections.
5.2 Hardware of the booster version
This is the schematic for one of the 16 columns of the booster version:
- The eight LEDs of the column are sourced from a 4.12V constant voltage
source. Via a current-limiting resistor of 22Ω those are driven by
an eight-Darlington driver IC ULN2801A. Its eight input pins are connected
to the output pins of a 4094. The segment current of each LED that is
switched on is roughly 20 mA. The numbering of the bits and LEDs is
symbolic, the actual bit- and LED-numbers can be derived from the component
placement plan below.
- The constant voltage of 4.12 V is made from the rectified transformer
voltage with a voltage regulator of 3.3V. The GND pin of the regulator is
tied to 4.12 - 3.3 = 0.82V. The regtulator drives currents up to 1A, from
which up to 50 LEDs with 20 mA each can be supplied.
- The left and the right part of the display drive 5 columns or 40 LEDs,
the middle part six columns or 48 LEDs. The supply for the middle part
has to deliver up to 960 mA..
- Each further column of LEDs requires an additional ULN2801A, in total 16
of those ICs are necessary.
Because the booster version drives the LEDs in Common Anode mode and because
the ULN2801A inverts the bits, no further inversion in the software is
necessary: the booster version functions exactly like the non-boosted versions.
Because the ULN drives LEDs only and no inductive loads, its COM diodes are not
needed and do not need to be connected, they are left open.
5.3 Power supply for the booster version
This here is the powerfull power supply for the booster version. A 30VA 2x6V
transformer delivers up to 5A, which are rectified and smoothed by two
10mF/16V capacitors. This supplies the 1A each for the generation of the
LED supply parts and for a small 3.3V/200mA regulator that supplis the
controller and the 16 pieces of 4094.
The maximum current, when all 128 LEDs are on, is available with this supply.
When operating under full load approximately 30€ costs per year for
electric power appear.
An alternative to this power supply, and somewhat simpler, would be to use
constant current drivers for the LEDs, such as CL2N3-G. The three 4.2V
power supplies as well as the 22Ω resistors would not be necessary then.
But: the CL2N3-G cost 45¢ per piece, and 128 of those would increase
the total price by 58€. That is by far more expensive than the
3-power-supply solution here.
5.4 Parts list for the booster version
These are all the necessary parts for the large booster version. Relevant for
the total costs of approx. 140€ are the LEDs, the two acrylic glass sheets
and the transformer.
5.5 PCB for the booster version
Two versions of the booster's PCB are provided here: a stacked version and a version
with all on one PCB.
5.5.1 Stacked PCB
This is the PCB for the booster version's current extender in a stacked version. It
is piggybacked onto the controller PCB, the 63 pins of the upper and lower as well
as the four pins of the pin headers fit into the female headers below. Thew stacked
version uses standard 160-mm PCB size.
By right-clicking onto the picture an enlarged version gif is available. The
drawing is included in the LibrOffice Draw file.
The PCB connects the inputs of the 16 Eight-Darlington-Arrays ULN2801A with the below
residing 4094 output pins. The outputs of the ULN2801As are connected to twin-lined
2x16 female headers, with which the display can be attached. The distance between
the two outer female headers is 16-tenth-inch (40.64 mm), the distance between the two headers
left and the two headers right is 15-tenth-inch (38.10 mm). Please note that the 22Ω
resistors have to be mounted to the display side, there was not enough space for
those on the Darlington PCB.
When wiring the PCB please note that the GND pins of the ULN (pin 9) all have to be
connected to the two middle pins of the 4-pin-header. As each ULN can sink up to
160 mA, not more than two ULN should use the same GND wire. That makes eight
connecting wires for the GND pins.
And also note that the two middle pins of the 4-pin-header have a different meaning
here than in the low-current versions.
This here is the related PCB placement plan. Please note that the output side of the
ULN all point to the 2x16 female headers.
5.5.2 All on one PCB
This PCB layout has all components on one large-sized PCB:
- the four controller types to select one of these,
- the 16 CMOS shift registers,
- the 16 Darlington arrays with the 128 current regulating resistors, and
- the four female pin headers to plug the display part's pin headers into.
The PCB has a size of 200 x 150 mm.
This is the component placement plan for all that. Like always: only the
desired version's components have to be soldered. And, of course, many
connections have to be made manually, because the single-sided PCB is
not fit to provide some of the connections.
When soldering the GND lines for the Darlington arrays, please be aware
that each array drives up to 120 mA through its GND pin, so do not wire
more than two arrays with a single wire.
Also here: right-clicking on the picture provides a higher-resoluted gif
file.
The somehow unusual size of the all-in-one PCB needs the connector
PCB for the display. Those who do not want to waste a photo-PCB for
that can use a standard lab card instead. The pin distances fit into
the hoöes of the lab card.
This is the related component placement plan. The two acrylic glass plates,
one with the mounted LEDs and one as background protection and for holding
the three foreground plates, are fixed on the soldering side of the PCB,
screwed with M2.5 screws to two glued wooden squared sticks.
The four male/female headers bring mechanical stability to the display
arrangement.
The three-pin terminal strip provides the anode voltages, directly connected
to the power supply.
©2022 by http://www.avr-asm-tutorial.net
This PCB layout has all components on one large-sized PCB:
The somehow unusual size of the all-in-one PCB needs the connector
PCB for the display. Those who do not want to waste a photo-PCB for
that can use a standard lab card instead. The pin distances fit into
the hoöes of the lab card.