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Ticker 16x8 logo

Text ticker with 16*8 LEDs and an ATtiny- or an ATmega-Controller

5 Booster version with a large display for the text ticker

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.

Design of a front plate for a large ticker with 10mm-LEDs

Drill template for the booster-LEDs 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

Schematic of one column of the booster version This is the schematic for one of the 16 columns of the booster version: 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

Schematic of the 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

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

PCB for the booster version 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.

Component placement on the booster PCB 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

Booster PCB version all-in-one This PCB layout has all components on one large-sized PCB:
  1. the four controller types to select one of these,
  2. the 16 CMOS shift registers,
  3. the 16 Darlington arrays with the 128 current regulating resistors, and
  4. the four female pin headers to plug the display part's pin headers into.
The PCB has a size of 200 x 150 mm.

Components on the all-in-one PCB 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.
Display connector PCB for all-in-one 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 hoƶes of the lab card.

Component placement on the display PCB 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.

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