Product Operation
This chapter contains manuals on how to use specific aspects of the LXA TAC.
Outputs OUT 0/OUT 1
The digital outputs are implemented using solid state relays, this makes them great replacements for situations where the functionality of a push-button or a jumper should be automated.
The LXA TAC outputs are able to read back the voltage between the output pins.
This can e.g. be used to measure the VCC of your DUT,
which is often present on a ~RESET line while it is not asserted.
Note
The OUT 0 / OUT 1 pins are allowed to float in voltage from the TAC’s
GND.
It is your responsibility to make sure that they stay within about
±25V of GND.
The outputs are not intended to switch large loads and are not guaranteed to work at frequencies above a few Hz.
The implementation of the voltage feedback measurement results in the
outputs being pulled towards GND with about a resistance of about
1MΩ even when open.
This may cause issues with very high impedance pull-up-resistors on
DUTs.
Usage of the digital outputs is best explained using examples for the three most common usage scenarios:
Using OUT 0 / OUT 1 as outputs
How to use a LXA TAC output to…
… control a jumper input
A jumper input consists of two pins on a 2.54mm pin header that are either electrically shorted using a jumper bridge or left open. Use two female-to-female 2.54mm pin header jumper cables and connect one to each pin of an output channel:
╭───────────────────────╮
│ LXA TAC │ ╭────────────╮
├───────────────────────┤ OUT 0 │ │
│ ╭╼┿╾────────╼┥ Device │
│ ╰╼┿╾────────╼┥ under test │
│ │ OUT 0 │ │
┆ ┆ ╰────────────╯
… drive a floating input
The LXA TAC does not apply a voltage to its output pins, as it is designed as a replacement for jumpers and buttons. To apply defined voltages to an input pin of a DUT you may use external resistors acting as pull-ups or pull-downs:
╭───────────────────────╮ 3.3V╭─────────╮
│ LXA TAC │ ╭─┨1kΩ┠────╼┥ │
├───────────────────────┤ OUT 0 │ │ Device │
│ ╭╼┿╾──────────┴──────────╼┥ under │
│ ╰╼┿╾─────────────────────╼┥ test │
│ │ OUT 0 GND│ │
┆ ┆ ╰─────────╯
Using OUT 0 / OUT 1 as digital inputs
Since the analog voltage over an output can be measured these pins can also be used as analog / digital inputs. How to use an output to…
… read back a DUT output pin
The output pin of the DUT can be directly connected to OUT0 / OUT1. Make sure not to assert the outputs, as that could damage the DUT or TAC.
╭───────────────────────╮
│ LXA TAC │ ╭────────────╮
├───────────────────────┤ OUT 0 DUT Out │ │
│ ╭╼┿╾────────────────╼┥ Device │
│ ╰╼┿╾────────────────╼┥ under test │
│ │ OUT 0 DUT GND │ │
┆ ┆ ╰────────────╯
The inputs can measure voltages with either polarity. You can thus use the two pins in each OUT 0 / OUT 1 pair interchangeably.
… DUT LED
Monitoring the status of an LED will usually require soldering
connections directly to the DUTs PCB.
LEDs are usually driven using a current-limiting resistor R.
You will need to identify this resistor and solder connections
to the PCB bypassing the resistor:
╭───────────────────────╮
│ LXA TAC │
├───────────────────────┤
┆ ┆
│ │ OUT 0 DUT Out ╭──────────────╮
│ ┝╾─────────────────╼┿──┬─┄ │
│ │ │ ┷ │
│ │ │ R Device │
│ │ │ ┯ under │
│ │ │ ┷ test │
│ │ │ LED │
│ │ OUT 0 DUT GND │ ┯ │
│ ┝╾─────────────────╼┿──┴─┄ │
╰───────────────────────╯ ╰──────────────╯
Using OUT 0 / OUT 1 as analog inputs
The ADC aspect of the OUT 0/OUT 1 aspect is useful for use cases like measuring voltage supply lines of a DUT to make sure that the device did in fact power down after cutting power to them.
Make sure not to assert the outputs when using them to measure e.g. a voltage supply as that could damage the DUT or the TAC.
╭───────────────────────╮
│ LXA TAC │
├───────────────────────┤
┆ ┆
│ │ OUT 0 5V ╭─────────╮
│ ┝╾─────────────────╼┥ │
│ │ │ │
│ │ │ Device │
│ │ │ under │
│ │ │ test │
│ │ │ │
┆ ┆ GND DUT GND │ │
│ ┝╾─────────────────╼┥ │
╰───────────────────────╯ ╰─────────╯