Multichannel Systems ME-System Manual - Manual (Page 21)

Welcome to (USB-) ME-Systems
21
2.8 Digital Input / Output, System Synchronization
TTL stands for Transistor-Transistor Logic. A TTL pulse is defined as a digital signal for
communication between two devices. A voltage between 0 V and 0.8 V is considered
as a logical state of 0 (LOW), and a voltage between 2 V and 5 V means 1 (HIGH).
Warning: A voltage that is higher than +5 Volts or lower than 0 Volts, that is, a negative
voltage, applied to the digital input would destroy the MC_Card. Make sure that you apply
only TTL pulses (0 to 5 V) to the digital inputs.
Important: Three BNC connectors for the digital input bits 0 to 2 are included in the standard
configurations of the ME-System with MC_Card. If you want to use more bits of the 16 bit input
channel or the 16 bit output channel, you have to order a
Digital IN / OUT Extension separately.
You can also upgrade your system with the extension later. Please contact your local retailer
for details. In USB based data acquisition systems, the 16 bit Digital IN / OUT connector is
available serially.
2.8.1 Triggering the Hardware and MC_Rack
The digital input accepts TTL pulses. This feature can be used for triggering the MC_Card and
USB based data acquisition devices and MC_Rack, for example, for synchronizing stimulation
and data acquisition.
For example, you can connect the SyncOut of a STG (stimulus generator) to one of the digital
input bits. If you use only one instrument for triggering, connect it to bit 0. In MC_Rack, add a
Trigger Detector to your virtual rack, and select the Digital Data D1 input stream as the Trigger.
Select the appropriate logical state (generally HIGH) for triggering. Mask all unused bits.
The standard settings of the Trigger Detector are for using bit 0.
Please see the documentation on the Trigger Detector instrument and on triggered data
in the MC_Rack Help or Manual for more details.
Important: It is recommended to set the duration of a TTL pulse to at least 200 μs. Shorter pulses
may be ignored by the hardware. Please mask unused (not connected) digital input channels in
the MC_Rack program to ignore undefined states of the open inputs that can cause unwanted
trigger events. Please see the MC_Rack Manual for more details.
2.8.2 Custom Switch for "Remote-Controlling" of the MC_Card
You can connect any device that produces TTL outputs, for example a switch, to one of the digital
input bits of the MC_Card. This means you can use a trigger for remote controlling the recording
with MC_Rack, or for synchronizing systems, if the data acquisition computer is not within reach
during an experiment.
You can define the time length of the cutouts that are recorded around the trigger event in
MC_Rack. Please note that it is not possible to start the recording of a continuous data file with
MC_Rack on a trigger, but you can start a new data file on the trigger event (select the Recorder
option Create New File On Trigger).
The following picture shows a suggested circuit diagram for a switch used for remote controlling.
The resistor and capacitor work as a low-pass filter on the TTL signal and are necessary to reduce
ringing of the signal.