Hi Folks,

New member, first post. I have been working my way through Charles Platt's book, Make: Electronics and have been fascinated by the chapter that has a SPDT relay as the heart of an oscillator circuit and modifying it's frequency output with a parallel capacitor. Being a amateur radio op, I am truly fascinated by all the varying types of oscillator circuits. On this one however, I am intrigued by its simplicity, yet certainly qualifies and works as an oscillator device. Does anyone know the history of this type of circuit- I'm thinking it may have originated in the devlopment of computer systems, but I'm wondering if someone intuitively knew that this device would make an oscillator or if someone just threw a bunch of parts together, possibly working on something else, and found that the relay could form the base of an oscillatory circuit and could be modified by a capacitor (sort of a tank circuit, I guess). Anyway, I'd really like to know if anyone has information on the history of this circuit and how it came to be?

Thanks much,

Dr. Dave, WS0D
Fort Collins, CO

 

Old car radios used vacuum tubes. They used vibrator power supplies to step 6V DC up to the required plate voltage (≈150V - 250V). I'm sure there were earlier uses of the same principle.

 

They were also used as a replacement to the Magneto an earlier version of the spark generator on the model T Ford in 1908, later to be replaced by the modern coil and points system. Coil

 

Ron,

Thanks very much for the info and link to this incredible site. I'm definitely old school with respect to radios/tv and this site is a gold mine of information on the old stuff. I am also fascinated by the early "rural" electric delivery systems used to get (or not) power to rural communities and farms- lot of history and a great tale of engineering development and evolution.

The car radio application is exactly what this relay circuit does on a small scale. As you note, I suspect that this application came after some earlier version- I just wonder if it was thoughtful design/engineering (as opposed to intelligent design;-)) or just a lucky circumstance where someone noticed, hey, this relay thing oscillates!

Best regards,

Dr. Dave, WS0D
Fort Collins, CO

 

DodgyDave,

Thanks also. Looks like it been around longer than me, and that's getting up there. Adding a parallet capacitor and then a variable capacitor has resulted in as you would expect, a change in frequency. I hope to be able to try and predict the frequency from a given capacitance, using calculations. Just need to look at it for a while and also do several more measurements of frequency vs. capacitance to see real world values. Thanks much, DD, Fort Collins, CO

 

I am part of this history

One of the first circuits I built as a kid was a bulb connected to a NC contact of a relay. I'd figure at the time that if I would use an LDR to switch the relay when I direct the light of that same bulb onto the LDR it would oscillate. It did . In fact the frequency depended I remember on the distance between the bulb and the LDR.

 

Relay oscillators are as old as solenoids and were used from the very first days of electricity. The solenoid movement was used to disconnect its own coil current.

I've seen relay based SMPS from the early war era (1940s?) that not only used the relay for oscillation/transformer but also for recification.

Even in the 1970's car makers used oscillating relay voltage regulators on cars.

 

Yoko - Very cool. That's bascially what I've been working on this weekend. I put together a resistance substitution box and then varyied the resistance in series with the capacitor. This altered the TC and the frequency of oscillation. Did you come up with an equation for predicting frequency by the varying values of the LDR?

RB- Thanks for the history. It seems that this is one of the oldest oscillator circuits around. I am finding it interesting as I can find various individuals who are associated with certain types of LC oscillators (Pierce, Colpitts, etc.), there does not appear to be one person who is ascribed to "inventing" the relay oscillator circuit or who was associated with defining its basic attributes and functions. I'll keep looking! DD in Fort Collins, CO.

 

This article says that Lenoir used "something like" the relay vibrator to generate the high voltage needed for ignition in his internal combustion engine.
I doubt that he invented it the vibrator.
The oscillating relay may have been invented in an "aha!" moment by someone. That event may not be recorded.

 

Wow, thanks Ron. This is getting closer. Literally, I'm from Cleveland originally, so reading about the K and W coils and their manufacturing site in the old Whitney building was fascinating. I sounds as if Ford went through an evolution that took them away from K and W's magneto, but then when they came up with their master vibrator coil version, they at least maintained a partial relationship. In the opening, the article says that part 2 of the series discusses specifically K and W, so possible I'll start searching here for more background history on the circuit development and its ultimate use as an ignition solenoid circuit. Many thanks, DD in Fort Collins, CO

 

Wow, thanks Ron. This is getting closer. Literally, I'm from Cleveland originally, so reading about the K and W coils and their manufacturing site in the old Whitney building was fascinating. I sounds as if Ford went through an evolution that took them away from K and W's magneto, but then when they came up with their master vibrator coil version, they at least maintained a partial relationship. In the opening, the article says that part 2 of the series discusses specifically K and W, so possible I'll start searching here for more background history on the circuit development and its ultimate use as an ignition solenoid circuit. Many thanks, DD in Fort Collins, CO

Did you notice that Lenoir invented his IC engine in 1862, and used the oscillating relay in it? This was before Ford was born.

 

...
The oscillating relay may have been invented in an "aha!" moment by someone. That event may not be recorded.

It might be possible to find some info from the earliest days of radio.

I think Marconi's first radio experiments used a single spark zap event, but it would have been VERY shortly after that they used multiple sparks from some type of solenoid buzzer.

The first ship radios (on the Titanic etc) used buzzing coils.

Somewhere in storage I've got an electrical engineering Uni textbook from about 1906, it's cute. They had almost no technology to teach about in EE then. From memory it has power transmission, some DC/AC motor stuff, and gyroscopes. Long before the days of valves or anythign technical. I can't remember if it has any radio stuff in it.

 

Did you come up with an equation for predicting frequency by the varying values of the LDR?

No, I was still in primary school at the time and wouldn't have had known at the time how to do this.