So I was going to try to surprise some people with this stupid idea. But it might be smarter to ask for help.
First let me explain the idea. Part of the reason I've always been fond of B-body GMs was my dad's uncle. For the last few years of his life his daily driver was an early 80s Caprice. He always kept 2 or 3 other B-bodies around but that was the one he drove. At some point the horn button quit working. His fix is what I'm trying to copy here.
He had the dialer switch from a rotary dial phone wired as his horn button. It worked in such a way that he could burst fire the horn up to 10 times by dialing that number.
I have never actually used one of those phones but based on how his setup worked I assumed I knew the component in question functioned. So I bought a switch from Ebay and then went to bench test the theory. What I got was a single long pulse and not the individual pulses I expected. This leads me to assume that different phones must actually work in different ways and as such I need to find a specific one.
So was I wrong assuming how these things worked?
Did I wire it wrong?
Is there a way to ID a switch that works like I need it to?
Is there a place I can find something else that works like I want it to here? I considered just using a turn signal flasher but it won't pulse fast enough to get the sound I remember.
I'm no help, I'm just posting to request a link to the YouTube video after you get it done!
I think you just have the switch action of the rotary dial backwards - it's normally closed and temporarily opens (turns off) the circuit when it passes a number.
Continued testing let the smoke out of the switch. Definitely need to do more research here.
This switch was probably never designed for 12 volt DC so a relay might be smart I think...
Your dad's uncle sounds like a pretty hilarious guy.
In reply to Keith Tanner :
He was. Unfortunately he passed I think 11 or so years ago.
RevRico
PowerDork
6/27/19 2:21 p.m.
In reply to Daylan C :
Phone lines run 5-8 volts dc if i remember correctly. So do most cell phone chargers, might be something to look at for testing.
I've used a rotary phone, but never really examined one to see how it worked inside.
ASSUMING it is a normally closed switch that needs 5 volts....
Use a USB charger type adapter to supply voltage through the switch to the signal input terminal of a normally-closed relay. The voltage will keep it open until the rotary switch opens, which will make the relay close, triggering the 12v main side of the relay. I think.
And it hurts me youve never used a rotary phone.
In reply to ultraclyde :
I'm 23. My family ditched landlines in general while I was in middle school.
Daylan C said:
In reply to ultraclyde :
I'm 23. My family ditched landlines in general while I was in middle school.
It's pretty unlikely those were rotary phones!
ShawnG
PowerDork
6/27/19 4:14 p.m.
Probably trips the ground of the horn relay. Relays can be NO or NC and used accordingly.
Lol. Yeah. I'm 43 and barely remember them. We probably ditched the last one in the early 80s when I was still in single digits. Just makes me feel old!
I agree with what others are saying - the rotary telephone runs on less than 12vdc. But just now I googled and got a lot of hits for how to make a rotary phone RING. But what you want to know is what the signal/tone pulse voltage WAS (back in the day) that is what the dial is working with. And it has been a looooooooooonng time since phone tech was not using tone signals. Because rotary dials were generating pulses not tones.
Anyhoo once you figure out what DC voltage to feed the dial and keep the smoke in, you just need to make sure that your horn relay can run OK with a signal voltage that low (assuming it ends up being a small value like 2-5 volts).
Call the Smithsonian Institute.
If you have a meter, you could figure it out with that. Set it to ohms, put the probes on two points, turn the phone dial, and watch your meter. Or listen if it beeps.
You’ll know you have the right two screws to attach your wires to when the meter pulses- jumping numbers or beeps/tones.
Maybe this will help?
Mind you, I have never taken one of these apart- but I sure want to now!
And I agree with everyone else, a relay and a separate power source are probably necessary.
Daylan C said:
In reply to ultraclyde :
I'm 23. My family ditched landlines in general while I was in middle school.
I'm with you, I'm 28 and my only experience with them was at my grandmothers camp built in the late 40's.
I didn't think landlines were a lost technology *quite* yet.
Phone lines are 48 VDC. Voltage isn't the issue here. The issue is current. Loop current is between 15 and 80 mA. Trying to run a horn, or even a beefy horn relay, may indeed let the smoke out of the dial. I'd be inclined to drive the horn relay with a FET.
The dial is a normally-closed switch, in series with the hookswitch. It "hangs up" the phone for a fraction of a second for each pulse. 1 pulse for a 1, ten pulses for a 0. The spec is 10 pulses/second, with a 66% break ratio. Using a FET as a relay drive would also let you invert the polarity of the signal, since what you want is normally open behavior.
EvanB
MegaDork
6/28/19 2:16 p.m.
Maybe this episode of the reassembler has some tips:
I still have a rotary phone where I work as a emergency back up . It still works on. POTS line and yes it is 48VDC at the line as ls3_mx5 mentioned although voltage does drop quite a bit when the phone is off the hook which it would've if you were dialing I can't remember offhand what it drops to though.
Funny story one of my tenants (an idiot) tried to power things with his phone line. He didn't have phone service but the line was still there for 911 access. The phone company was not impressed.
While we're on the subject, because of the fact that rotaries dialed by breaking contact, you could actually dial a number with a button phone by tapping the hang up switch in just the right pattern. Fun info.
EvanB said:
Maybe this episode of the reassembler has some tips:
Fascinating show that I can’t imagine many will watch. I sure will. The yard will have to wait.
ls3_mx5 said:
The dial is a normally-closed switch, in series with the hookswitch. It "hangs up" the phone for a fraction of a second for each pulse. 1 pulse for a 1, ten pulses for a 0. The spec is 10 pulses/second, with a 66% break ratio. Using a FET as a relay drive would also let you invert the polarity of the signal, since what you want is normally open behavior.
....and because of this, you could dial out of some payphones for free by tapping the number out on the hook.
What is really fun is how looooong it seems to take for a modem to dial out when commanded with ATDP (pulse) instead of ATDT (tone). Because your family was too cheap to spend the extra five bucks a month for touch tone service, in the 1990s.
