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Addendum

Using Low-current Devices with the Zeus GPI Outputs

Document: Zeus Getting Started Manual, Rev A

Addendum Number: 1

General Instructions: Use this addendum with Revision A of the manual. This information will

be included in Revision B.

Subject: This addendum includes additional information about the use of the GPI outputs. It can

be used together with the GPI connector pin-out information in the Specifications section, page

10, and the GPI connector information starting on page 28.

A ULN2803 device driver IC is used for the GPI outputs of the Zeus frame. This IC has 8

outputs, each of which is capable of sinking up to 500 mA at 5 VDC. However, the Zeus internal

power supply cannot provide enough power to simultaneously drive all 8 outputs at their

maximum rating. The total drive current for all outputs should be limited to 400 mA. That is why

the Zeus manual shows the use of an external power source and switching transistor (Figure 24,

page 28 of the manual).

On the other hand, some relays (such as the Takamisawa AS5W-K) only require about 50 mA. If

eight of these relays are used, all 8 GPI outputs can be driven at the same time. In this case, the

external drive transistor can be omitted, and relays can be connected as shown in Figure 1,

below.

Common

GPI OUT +

Figure 1. Direct connection of a low-current relay to a Zeus GPI output. Also connect a switching

diode to protect the output from back EMF. (Diode is included with the Takamisawa relay and may

be included with others.)

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RTS TM-2000 Manual do Utilizador Página 34