There are a number of communicaton transceiver chips that are used for the
DMX protocal.
DMX is basically a command set that uses the RS485 standard. When dealing with the transmission and receiving of
DMX signals, the chips or ICs should be RS485 compatible. I have found three different families of ICs that qualify.
I am not
book or school educated on the subject, but while rebuilding
Wybron scrollers and
power supplies, I discovered that there were more than just the 75176 ICs used in
DMX signals. Upon searching suppliers for the 485 ICs that
Wybron uses, I discovered that there is a third family of ICs, that falls between the 485s and 75176s in price. I believe, but I am not sure that Digikey carries all three. Mouser only carries the 75176 and 485 lines. When in question, I checked the data sheets on all three lines, and found the pin assignments the same, and most of the electrical specifications to be the same. I have used 75176 ICs to replace all of the other more expensive RS485 ICs with no problem.
The important thing to observe when purchasing from Mouser, is that the ICs have through hole pins and are not surface mount. Because almost all of the 75176 ICs listed at Mouser are of the same manufacture, but different prices, it can be confusing as which ones to
purchase. I usually
purchase the ones that are just one down from the most expensive, and if I am purchasing just a few I will
purchase the 485 ICs.
Having now said that I would expect at least 6 people to respond that I should use some sort of more scientific method of choice in the
purchase of these ICs. I have yet to have a problem with any that I have used.
In helping out 5 or 6 theatres in our area, I have gone through quite a few 75176 ICs. They seem to be the item that gets sacrificed during a lightning storm to save the rest of the circuitry. I just got through repairing 12
Wybron Forerunner scrollers, where everyone was just the Communication IC. One of the units had the chip and
socket completely burned off the board. They all went out during a show and during a storm. The
console also lost two of the three ouputs in that storm and replacing the ICs was all that was required for the repair.
The
theatre that I repaired the
console and scrollers repaid me by buying me 75 of these ICs. I am retired and I don't charge them anything for the repairs, but they purchased these ICs as a jesture of thanks. I think that I am ready to handle the community of theatres for a while.
