Stop Ring Voltage from reaching device (Phone, Modem, etc...)
I am sharing a POTS line with a MFD device and an outgoing-only fax modem. The fax modem is on an unsupported RISC box with unsupported proprietary fax & ERP software. We need the ability to occasionally send faxes from the unsupported (legacy) system to get old invoices, purchase orders, etc. The problem is that the fax modem answers on the first ring. The MFD does not have get a chance to pickup the line. We have no need for the fax modem to answer any incoming calls. I have no idea what the required modem string is to properly set this fax modem for the proprietary software. I have set the register zero to zero (ATS0=0) but then the fax modem stops working entirely. I know the proper "fix" is to send the entire correct AT command string including the ATS0=0 but, because we no longer have support on the software, the software company will not provide any help. I'm hoping there is a down and dirty analog circuitry work-around but don't have the skills to design it myself. Back in the day, I may have been able to but I have forgotten most of what I knew about analog circuits... So, finally, the question; Is there a simple way to stop the ring voltage from reaching the answering device (fax modem in this case). I'm thinking some sort of a diode across tip and ring? Maybe a resistor or load to drop some voltage? I don't have a test bench here to experiment with solutions so hoping one of you real engineers will provide a quick answer!
Many thanks - Sorry for the long-winded post! Lon
