3 ms·
Cool! > One of the disappointing things is that it is not possible to make the phone ring because the ringer requires a much higher voltage than can be generat
by hunter2_ 5y ago
Cool!
> One of the disappointing things is that it is not possible to make the phone ring because the ringer requires a much higher voltage than can be generated by a small computer.
Voltage can be stepped up using a transformer, no problem. It's that you need 20~25Hz AC and a certain amount of current (see "ringer equivalent" calculations). Either way, you're probably right to skip it for this project :)
- jcims 5y agoI think anyone that was busy wrapping their phone line around a terminal when a call came in would agree. :)
- vidarh 5y agoWe had a little mini-thread on getting shocked when a call comes in just yesterday: https://news.ycombinator.com/item?id=29613712 https://news.ycombinator.com/item?id=29613712
- jacquesm 5y agoI built my first modem from discrete parts and the first time a call came in on that line the whole thing went up. Major design oversight :)
- danachow 5y ago> because the ringer requires a much higher voltage than can be generated by a small computer. I mean that’s not quite true. A magicjack which is basically an ATA is about the size of the Pi Zero and produces ring power. A REN is on the order of 10 mA which at 90V can be generated by a very small (like smaller than a dime) switcher. Indeed the quickest and easiest way to “modernize” an old phone is probably to stuff the guts of a readily available analog telephone adapter and interface it to a Pi, or a Wi-Fi adapter, etc. You might even dispense with the pi: https://randywestergren.com/reverse-engineering-obi200-google-voice-appliance-part-2/ https://randywestergren.com/reverse-engineering-obi200-googl...
- rileyphone 5y agoThis + an ATA like the PAP2T is the easiest way: https://www.oldphoneworks.com/dialgizmo-pulse-to-tone-converter.html https://www.oldphoneworks.com/dialgizmo-pulse-to-tone-conver...
- ale42 5y agoFor the problem of converting pulses to tones, some time ago I made a small circuit that generates the DTMF tones directly inside the phone. It's basically an interface between the rotary dial and the phone line, based on a simple 8-bit PIC microcontroller powered from the phone line (actually coming from an ATA). The idea is to publish it as open source hardware as soon as I find enough time to document it... Downside is that you have to solder it (SMD components) and put it inside the phone...
- danachow 5y agoThe very affordable grandstream ATAs will handle pulse without additional hardware. http://www.classicrotaryphones.com/forum/index.php?topic=20386.0 http://www.classicrotaryphones.com/forum/index.php?topic=203...
- Aloha 5y ago90v at 20-30hz and about 20ma I believe. Normal phone lines will supply upwards of 100ma, but since you only need to ring one ringer, you can do with less, you can also tune the ringer to make it more sensitive.