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    • #7413

        Hi all,

        A component I haven’t used yet of our start and expansion set is the relay.

        Time to change that ! The relay is such a versatile component and since I love to tweak and invent, let’s make some cool circuits with it !

        Besides the circuits proposed in the manual, here are some more fun and crazy experiments.

        For our legacy Lectron users, I will try to publish the same circuits with the legacy PNP transistors.

        Just pay attention to the correct positioning of the blocks (+ & – are reversed).

        Since I have only the new version of the relay, maybe users with the legacy version can comment if these circuits work.

        When I look into the new relay block, I see a small relay operating with 5 Volts ! Have the legacy relays also this working voltage ? Strange, since our power supply is 9V ! So, I believe care must be taken in circuit design or the coil may burn due to the higher current.

        Well, let’s start with a funny experiment, a relay blinker, which resembles the direction blinker of a car.

        And what’s even funnier, we can also alter the speed of blinking, from slow to ultra fast !

        This is the version with the new NPN transistors :

        Relay blinker NPN

        And here with the legacy PNP transistor:

        Relay blinker PNP

        As protections, we use a 120 Ω resistor in series with the emitter of T1 for the relay and a 47Ω resistor for the lamp.

        The circuit is fairly simple.

        With the relay in rest position, C1 is charged through P1. When the voltage is high enough, T1 starts to conduct, pulling the relay.

        Now, the relay changes it’s contacts and C1 discharges through P1 to the ground.

        The situation repeats itself. Since P1 is responsible for charging and discharging C1, altering it’s resistance influences the blinking speed.

        Feel free to experiment, add more resistors to the circuit, use other capacitors, …

        Happy blinking !



      • #7424

          Hi Frank,

          great idea to use relays because their function is quite simple to understand – and they are still working in many applications around the car / house / machine area – thanks!

          The history of the Lectron relay:

          • since 1966 a component of the “Ausbausystem 2” set: 300 Ω, 9V, without diode = #8054 / #8100502
          • since 1975 with “Funktionsmodelle” a second version for 5V, 70 Ω, (TTL driven) without diode, #8100506
          • undated: Mr.Birett had built a prototype with one diode for Physics teaching
          • undated: Mr.Gürth used his own version to store 1 bit (TTL introduction)
          • until the 199x years both versions were available, but with different relay types: 70 / 130 / 180 Ω
          • since 2001 (RWO) the actual version with diode: 5V, 70 Ω, as #2504



          • #7426

              Great history on the relay Günther, I did not know most of this information until now!

              I am going to have to find an additional place for this information.  Perhaps where I write about the battery, meter, and speaker blocks.

              Thank you for your insight!


          • #7427

              Hi all,

              Guess what ! The relay that came with my 1205 set (2504) is indeed a 5V relay but there’s no diode mounted on the pcb inside the transparent cube
              So I thought, maybe the diode is inside the relay. The relay manufacturer states that there’s no diode mounted inside the relay.

              The idea using a 5V relay has its advantages. It’s more sensitive and you can build your circuits using resistors or other components in series with it.

              I still believe that our battery voltage (and certainly with the power adapter) is way too high.

              When using a resistor of 120 Ohm in series with it keeps the voltage at 5V across the relay and will save our battery life !

              It is probably the best to adapt the experiments in the manuals. Since the white cover has rather fragile tabs, I don’t like the idea to change the relay when broken.

              Time to do some tests about the diode. Is it there or is it not ?
              I keep you guys informed.



            • #7429

                Hi all,

                Thank you Guenther for your relay overview !

                Something to take in account with when designing circuits !

                The test results of the RWO relay :

                There is no diode in the module 😯

                First of all, I measured the coil resistance which is about 70 Ohm like Guenther mentioned.

                Then I set up a simple circuit : battery – 120 Ohm resistor – switch – relay. I used my oscilloscope on single trigger and measured the fly back pulse across the relay coil when operating the switch.

                Indeed, we have spikes up to 40 Volts. So, by adding an external diode across the coil, this spike was completely suppressed.

                Uh oh, we really need this diode to protect our semiconductors …

                Is this a coincidence ? As far as I can see, there’s no place where it can be soldered on the PCB.

                Can someone check with their relays ?

                I hope I have warranty on this …



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