After a full day of planning and another day of soldering, it was finally time for the moment of truth: powering my circuit.
I started cautiously. I grabbed my multimeter and checked the most important points, specifically where the power enters the board. No short circuits. Everything looked clean. I took a deep breath and plugged in the 9V DC supply.
And… nothing. Of course.
After some more measurements with the multimeter, I found a few cold solder joints. I resoldered them, held my breath, and tried again. Success! The 9V DC circuit was humming along perfectly.
Fire!
Suddenly, the circuit breaker for my entire room tripped. My transformer was broken… again. To make matters worse, a literal flame shot out of my power strip.
I’m not going to lie: I was terrified. I thought I had built a fire hazard instead of a telephone exchange. I didn’t want to touch anything anymore.
Back to Basics
I had to know if I had destroyed my hard work. I went back to step one: I disconnected the power supply and hooked up a simple 9V battery. The result? The circuit worked perfectly. So where did the fire come from?
A second opinion
I managed to get an engineer to take a look. After explaining the flame situation, his verdict was a huge relief:
“This wasn’t caused by your low-voltage circuit. A flame and a tripped breaker on the 230V side mean the fault was inside the power adapter itself, not your board.”
It turns out the AC-to-DC converter I was using was likely faulty or poor quality. This also explained why I had so much “hissing” noise on the phone lines earlier, the power supply was “dirty”.
I swapped it out for a new adapter, plugged it in, and… it worked! No flames, no tripped breakers, just a clean-running circuit.
The AC Ringer
Even though the 9V side is stable, I’m still dealing with some post-traumatic stress from that flame. I haven’t dared to test the high-voltage AC circuit (the part that actually rings the bells) yet.
I’m pushing that stress off until Wednesday. I can’t hide from the ringer forever, but for today, I’m just happy I didn’t burn the house down.