This page covers two boards: a slow octal open collector driver board and a fast octal TTL 50 Ohm driver board.  Both boards optically isolate the host the National Instruments ("NI") 6602 Counter/Timer module from overloads, shorts, reverse voltages, transients, galvanic errors such as ground loops, etc.  Although not idiot-proof, they are reasonably robust and failures of almost all types on these boards will not damage the 6602.  They connect to the 6602 by ribbon cables connected to a NI SCB-68 breakout box.  Neither the 6602 or these boards will be damaged if both are not turned on and powered up, power sequencing is not important.  Both boards have passive isolated TTL voltage inputs, specifically an LED from a photo-isolator via 330 Ohms to ground per channel.  Each input requires approximately 3mA source.

Open-Collector Board

The Open Collector board drives loads such as relays, lamps, solenoids, etc.  It can also be used on devices that require switch inputs connecting the input to its common or ground reference.  It has eight independent channels, each one turned on by a logic "1" at the channel's input.  An external power supply of +5V to +30V is used to power the photo-isolators and to clamp transients from inductive loads.  Inductive loads should be bypassed as close as possible to the load with a diode or RC snubber.  If multiple supply voltages are required, the highest should be connected to the board.  Check schematic for updates, however following is for reference: each channel is rated at 30 V max and about 400mA but derated pro rata to 150mA if all eight channels are used.  The schematic is in Eagle software and also available as a PDF.

TTL 50 Ohm Board

The TTL 50 Ohm board drives TTL loads through 50 Ohm transmission lines or discrete wiring.  It can be used on any device requiring TTL voltage inputs.  Outputs are on BNC eight isolated connectors.  Each channel's output has a 43 Ohm resistor in series with it plus a 4.7 Ohm resistor isolating the BNC return to a common ground potential.  This ground potential is connected to the external power supply's negative terminal and may be left floating (preferred) or connected to earth.  If possible, do not connect the transmission line's shield to anything but the load (device being driven) as this will let the grounds float (at 4.3 Ohms above the common ground) and reduce ground loops.  Also if possible, do not ground the load.  If additional voltage swing is required, do not add an external pullup resistor as this may damage the board if the board is powered down and the external pullup source is power up, rather modify the channel on the board for a pullup.  The schematic is in Eagle software and also available as a PDF.

Return to homepage        Please report broken links, problems, corrections and suggestions to astummer_at_physics.utoronto.ca. Last updated 11 August, 2005 .