Dabbling in Electronics

[RogerH]

I like to dabble in electronics. It started in apprx 1968 and I've never got bored with not having a clue at what I'm doing.

I was an engines/Airframe apprentice at BEA but soon found that dabbling in the unknown was fascinating.

Some of you may know that I make an Overdrive Logic box for the TR A and J types. In this case logic is a poor name.

Anyway it started as a simple 2x relay some wire and a diode (oooh technology)

As members reported issues I would improve it to remove any weaknesses.

My latest incarnation has a Thyristor ( a sort of solid state SPST relay). and this was used in conjunction with a small power TRansistor to turn on and OFF.  Turning off a Thyristor is not that easy ( honest )

Everything was huncky dory until I found that occasionally the device would not turn off - hmmmm  or perhaps ON.

I then replaced the power tranny with a power MosFet. This is like a power TRanny but spelt differently.  It also has some rather miraculous characteristics that I will not bore you with.  

This new device worked perfectly - except (oops)  when coming out of OD into another gear it would come back on by itself - aaarrrgghhh

I scoured the interweb for an answer on how to turn OFF the Thyristor and kept getting the same answers that were no good for me.

So thinking cap on.  With the Thyristor ON and you now disconnect the earthy end of the circuit it turns OFF.

If you now reconnect the earthy end it turns back ON - This should not happen.   Basically The Thyristor is ticking over and not fully turned OFF.

So when the earth is reconnected it bounces back to life without being told to do so. (little bu99er)

What my head scratchjing came up with was to feed a 12V supply into the earthy side of the thyristor via a 1K resistor

So now when you go into neutral from OD the earthy wire from the Thyristor jumps to +12v (only 0.012mA going through the resistor)

This stops current flowing through the Thryristor because you have the same volts at both ends  of the Thyristor and it turns OFF.

A simple little restistor sorted it.  But you won't find it on the InterWeb

If any body has one of my boxes (I know of one member) and has any problems then you can exchange it for a super technological marvel

I wonder what a normal life is like

 

Roger

 

 

 

 

 

 

 

[rogerguzzi]

Hello Roger

                    All that above my pay scale !!

But I have two of your old! boxes one fitted to Spitty(which works perfectly )  the other waiting to fitted in the Vitesse !! (plus a good friend runs one as well!)

but if you want me to send it back for the Super upgrade I will and fit it to Spitty for a good testing next year(Spain booked for June and hope to talk Memsahib into a second trip later!!

I am a bugger for trying new bits like you do its bit like tweaking engines because you can it's not about the power(to me it's engineering type things Spitty seems to go well and can hold her own if in the right gear at the time(but does not have the flexibility of your sixes so requires skill??Luck? foot down in lower gears then she surprises them!

roger

[RedRooster]

Interesting, I thought it was done with a flip-flop circuit? 

[RogerH]

4 hours ago, RedRooster said:

Interesting, I thought it was done with a flip-flop circuit? 

My feet do not get on with flip-flops.

Some may do but mine is different.

 

Roger

[RogerH]

8 hours ago, rogerguzzi said:

 

but if you want me to send it back for the Super upgrade I will and fit it to Spitty for a good testing next year

 

roger

I will run one in my 4A over the winter to make sure it works for a good length of time.

I'll send it to you in early spring. It is a direct swap.

 

Roger 

[yorkshire_spam]

My electronics stuff is almost completely digital stuff - although I learned about op-amps and stuff at Uni I struggle with the analogues side.

Here's my old work-bench for digital:

[RedRooster]

41 minutes ago, RogerH said:

My feet do not get on with flip-flops.

Some may do but mine is different.

 

Roger

Banged it into AI, flip flop out put from a momentary switch. 

## Flip-Flop Circuit for Momentary Switch

A **flip-flop circuit** that changes state with a momentary switch is often designed using an SR (Set-Reset) flip-flop or a JK flip-flop. Below is a description of how to create this circuit.

### Components Needed:
- **SR Flip-Flop or JK Flip-Flop Integrated Circuit** (e.g., 74HC74 for SR or 74HC109 for JK)
- **Momentary Push Button Switch**
- **Resistors** (e.g., 10 kΩ)
- **Capacitor** (optional, for debouncing)
- **Power Supply** (typically +5V)

### Basic Diagram Explanation:

1. **Power and Ground Connections**: Connect the VCC pin to +5V and the GND pin to the ground.

2. **Switch Connection**: Connect one terminal of the momentary switch to the **Set (S)** input of the flip-flop. Connect the other terminal to ground.

3. **Reset Connection (Optional)**:
   - If using an SR flip-flop, connect a resistor to the **Reset (R)** input to pull it high when the switch is not pressed. 
   - If using a JK flip-flop, connect the **J** and **K** inputs appropriately.

4. **Debouncing (Optional)**: To prevent multiple toggles from a single press, add a small capacitor in parallel with the switch.

5. **Output Connection**: Connect an LED or other output device to the output pin (Q) to visually see the state change.

### Example Connection for SR Flip-Flop:

1. **VCC**: Connect to +5V.
2. **GND**: Connect to ground.
3. **S (Set)**: Connect to one terminal of the push button; the other goes to ground.
4. **R (Reset)**: Connect a pull-up resistor (10 kΩ) to +5V.
5. **Q**: Connect to an LED with a current-limiting resistor.

### Operation:
- Pressing the momentary switch sets the flip-flop, changing the output state from low to high.
- Releasing the switch retains the state until the switch is pressed again (if designed for toggling).

---

This setup allows the flip-flop circuit to toggle states with each press of the momentary switch. If you need further elaborations or specific circuitry for JK flip-flops, let me know!

[RedRooster]

https://www.amazon.de/Tyenaza-Bistabiler-Selbstverriegelungsschalter-Niedriger-Boarding/dp/B0983MCWWK

 

[RogerH]

Oh no. What have I started.

 

Roger

[egret]

Is this a pulldown resistor?

In the latest Binky video (where they are so far down the electronics rabbit hole they might very well be in the earths core), they talk about pull up/pull down resistors, which are used to ensure that the voltage on an open switch reverts to what you want.  These are used extensively in the speeduino (and I'm sure all other ECUs and electronic devices) to ensure that logic states that are wanted are achieved i.e. the thing you want sits at the voltage which relates to a 1 or a 0. 

My understanding is that a pulldown resistor basically connects the switched outlet to ground.  So when the switch is closed, a pulldown resistor operates as a resistor and limits current flow allowing the logic output to remain at the hi-voltage state, but when the switch opens it allows current to flow between the logic output and ground to dissipate the voltage.  The analogy in the binky video is that they operate like a return spring on a throttle returning your logic signal to the required state (pullup being to hi, and pulldown being to ground).

This is a level of electronic circuit design knowledge above my previous understanding, and sort of makes sense.  Turns out learning about electronic circuits and logic control is more interesting when the end result is horsepower! Who knew  

Might be interesting reading if you're that way inclined!

https://en.wikipedia.org/wiki/Pull-up_resistor

[JohnD]

Oh, that way madness lies; let me shun that!

[RogerH]

3 minutes ago, egret said:

Is this a pulldown resistor?

In the latest Binky video (where they are so far down the electronics rabbit hole they might very well be in the earths core), they talk about pull up/pull down resistors, which are used to ensure that the voltage on an open switch reverts to what you want.  These are used extensively in the speeduino (and I'm sure all other ECUs and electronic devices) to ensure that logic states that are wanted are achieved i.e. the thing you want sits at the voltage which relates to a 1 or a 0. 

My understanding is that a pulldown resistor basically connects the switched outlet to ground.  So when the switch is closed, a pulldown resistor operates as a resistor and limits current flow allowing the logic output to remain at the hi-voltage state, but when the switch opens it allows current to flow between the logic output and ground to dissipate the voltage.  The analogy in the binky video is that they operate like a return spring on a throttle returning your logic signal to the required state (pullup being to hi, and pulldown being to ground).

This is a level of electronic circuit design knowledge above my previous understanding, and sort of makes sense.  Turns out learning about electronic circuits and logic control is more interesting when the end result is horsepower! Who knew  

Might be interesting reading if you're that way inclined!

https://en.wikipedia.org/wiki/Pull-up_resistor

That sounds about right.

In my case I wanted to stop the Thyristor ticking over so that it was OFF.

However if you keep the power applied to the Anode (the front hot end)  and cut the earth you will stop normal power operating whatever device you have but the Thyristor is still lurking.
So when you remake the earth (but you do not necessarily want the Thyristor ON) the Thyristor does in fact power up and turn ON fully.

By having the pull up resistor on the Earthy kathode  when the Thyristor is ON everything works as it should. The pull up resistor will pass 12mA but has no effect.

However with the Earthy end open circuit the pull up resistor puts 12V on ther kathode so both sides of the Thyristor now 12V and stops current flowing - even the stuff that is lurking.

To answer RedRoosters point - yes  a Flip Flop (Invented by the Frenchman Philip Philop) will do that basic function.

My circuit has my version of a FF  but it is fashioned as a time delay switch.   The Thyristor and MosFet are required to shift the load
in my case 400mA but it could be as high as 35A.

I did use relays for this part of the circuit but they were not shake proof and could easily change state over a pothole.

 

Roger
 

 

 

[RedRooster]

Didn't think about pot holes to be honest. 

[Nick Jones]

2 hours ago, RogerH said:

a Flip Flop (Invented by the Frenchman Philip Philop)

🙂Not many people know that 😛

[RedRooster]

1 hour ago, Nick Jones said:

🙂Not many people know that 😛

Quite ahead of his time Philip. 

[RogerH]

[DeTRacted]

On 11/16/2025 at 5:03 PM, RogerH said:

If you now reconnect the earthy end it turns back ON - This should not happen.   Basically The Thyristor is ticking over and not fully turned OFF.

if there was no current flowing through the thyristor when the earth was removed it  probably was turned off but the transient current spike through internal capacitance might have turned it back on when you re-made the earth connection.  Thyristors are rather prone to dv/dt switching when power is applied suddenly*.  Your pull-up resistor might just be slowing things down enough to prevent that.

 

* Back in the very late '60s  a (considerably richer) friend of mine bought a brand-new Ford Corsair and after some months decided to build himself an anti-theft device for it, based on a thyristor which was used to somehow short out the ignition circuit to prevent the engine being started. It seemed to work well after installation until the first time he actually did start the engine, at which point the ignition spikes tripped the  thyristor which latched fully on.   The first indication of this was that the engine promptly stopped again - accompanied shortly afterwards by clouds of acrid white smoke from under the dash.   Only swift disconnection of the battery saved the day and luckily everything still worked when the immobiliser was removed.   He didn't keep that car for very long after that. 

[RogerH]

Hi Rob

 many thanks for that

The Thyristor was fully ON when the earth was rapidly removed.
This appeared to turn it OFF

But when the earth was remade (before fitting the pull up resistor) the Thyristor came fully back ON

With the pull up resistor fitted it did not come back ON.    Suggesting that it was fully OFF.

 

Roger