The I/O Filter WildcardTM
|Fig.1||I/O Filter Wildcard Schematic showing positions for through-hole components. For each through-hole component (e.g., labeled 1A, 1C, 1E, 1G) there are also parallel pads for surface mount components (e.g., labeled 1B, 1D, 1F, 1H) not shown here. Of the 24 identical channels, channels 1, 2, 3, and 24 are shown.|
Up to four through-hole or surface-mount components may be connected per circuit, or if both types are used up to eight circuit components may be used as shown in Figure 2. Some components connect the input pins to the output pins, while other components connect the signal path to either of two rails, a top rail, generally used for the positive power supply, and a bottom rail, generally used for the circuit ground.
Figure 1 also shows several options for deriving the top and bottom rails. The top rail may be connected to the +5V or the V+RAW supplies by jumpering the pads (i.e., connecting a wire or zero ohm resistor) labeled V+ or +5. Similarly, the bottom rail can be connected to the Wildcard Bus ground, but jumpering the GD pads, or to a user supplied input on pin 3 of H2, by jumpering V-. The user supplied input would be generally used if a negative voltage is desired.
These rails may be filtered by using resistors or inductors in place of the zero ohm jumpers and installing capacitors at positions F1 and/or F2. Or they can be protected against overvoltages by installing appropriate protection devices (such as zener diodes, SIDACTORs, or GDTs) at F1 and/or F2. Further, the rails may be derived from any of the input or output pins by installing shorts in appropriate component positions in the circuit of Figure 1.
Figure 2 shows each of the twenty four circuits in more detail, showing the parallel pads for surface mounted components.
|Fig.2||Each set of holes for through-hole components is connected to a parallel set of pads for surface-mount components. Either type of component may be used, or both used for as many as eight components per circuit.|
Figure 3 shows several of the most commonly needed filtering circuits.
|A)||Often voltage attenuation may be needed for A/D measurement as shown in Figure 3A. Resistive dividers are produced simply by inserting through-hole resistors at locations nA and nC for circuit n.|
RC filters are very useful as anti-aliasing filters when using the Analog I/O Wildcard. |
Figure 3B shows the most simple of these.
|C)||Sometimes an input signal should float to an intermediate voltage between power and ground, or it should be shifted as well as attenuated, as shown in the circuit of Figure 3C.|
|D)||If an input exceeds the voltage levels allowed by your controller or Wildcard, you can clamp the input to the power supply rails using Schottkey diodes as show in Figure 3D.|
|E)||The I/O Filter Wildcard can also serve as a general purpose prototyping board. Figure 3E shows the creation of a 2.5V reference on I/O pin 5 using a precision voltage reference chip and the 5V supply.|
|Fig.3||Several of the many input/output filters and other circuits that can easily be configured.|
Figure 4 (click to open in a separate window) provides a larger-than-life diagram of the top and bottom of the I/O Filter Wildcard so that you can easily see the positions and labels of the components. The large central region provides holes for through-hole components while surface-mount components use the periphery.
The board's silk-screen legend provides the same information, but the print isn't always legible. You can use Figure 4 as a guide when soldering components to the board. Through-hole components are mounted in the large central region while surface-mount components are mounted in the peripheral areas. Note that the shapes of the through-hole pads, round or square, correspond to the connection symbols used in Figures 1-3. You should pay attention to these shapes when wiring polarized components.
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