Note: This type of switch with few alterations can be used for any other project as well but is designed based on e-bike needs!
Introduction to the project
There are several problems with the standard key switch of the e-bike battery. Usually manufacturers place a cheap key lock switch.
The first disadvantage of this type of switches is that can be easily violated with a screwdriver or by using professional thief key technics.
Another headache is to keep always the key on you and try to not lose it while you are away from home.
Also the key looks too ugly and obsolete in our modern digital days.
This solution has protection feature from accidental switching OFF action. More about this later on.
Although the appearance of 9 square formed buttons (Keypad) looks digital and complicated, this circuit
is so simple that anyone can build for his bike with just the basic electronics knowledge. You even don't need a PCB.
At the illustration I have made the physical circuit diagram to make your life easier.
Just 7 components are being used here.. 3 thyristors (BT169 or any other similar type can be used),
3 resistors, 1 latching relay type HFE10-2-12-HT-L2, and a ready build DC/DC converter.
The thyristors and resistors are easy to find at your local area but the specific relay is a bit difficult.
You can buy it from the net or you can use a similar type available to you!
The DC/DC Step Down converter is a known Chinese Module that provides 3A continuously. Is a Non-isolated Buck Converter and
auto-stabilizer with fixed output of 9V or 12V (choose 12V).
The input voltages have two options 16-90V or 16-120V (any will do.. I use the 16-120V type).
It has very low power consumption and great conversion efficiency of ~96%.
The smaller the differential input/output voltage, the higher the efficiency.
You don't need numbering or letters on buttons.
You will memorize the code sequence by your photographic memory once for ever. The coding settings will be explained later.
If you want to change the sequence code, you can change the buttons position as you like to be.
At the diagram I intentionally placed numbers on the buttons randomly so to explain the functionality of the circuit.
You can alter the position of the switches to change the code as you like as long as you keep the correct wiring.
Before you start
Make sure you have space on your bike!
All has to do with the available space you have to hide the relay and the tiny module.
Keep in mind that the relay should be close to your thick power wire (usually red) that is coming from the BMS to your controller.
Between this distance you should find a place to secure the relay.
The positive (red) wire will be cut and soldered on relay or removed from old key switch if exist and will be substituted by the relay, wired as the diagram shows.
This type of project fits more for custom made battery casing that can have more space to hide things inside.
In my case the aluminum top casing cap was made intentionally taller 5cm at the front.
to hide more converters and chargers along with the bike's alarm and the GPS-Tracking module.
Starting from the buttons (dark red at image) that can be any waterproof type of button that fits well to your bike.
Place buttons physically close to look more like a keypad, this keeps passing thieves away and looks cool too.
Measure your button diameter add 2-3mm spacing between them and find the distance of their centers.
So now you can take the ruler and mark the 9 centers on a peace of paper.
Cut the paper parallelogram and place it on the position you want the buttons.
Stick the paper stable and use a center punch to mark the holes on casing. Open the holes and place your 9 buttons.
You will not need actual PCB for this circuit so your PCB is your buttons back.
Solder the resistors and the thyristors as you see it on the diagram. Keep the wires clean and as short as possible.
You don't want a wire mess in there. Use hot glue to secure flying wires etc.
Secure the relay and the DC/DC module where you need them and connect them accordingly following the diagram.
In my case the relay is placed at the far back near the controller
and the DC/DC converter is placed near the keypad buttons.
Keeping in mind that cables adds weight, keep them short.
It will be easier accessible later if needed.
Instructions, Coding and Settings
This project use a clever functionality of thyristors to create a sequential pattern.
Button 7 passes current to the second thyristor and button 2 passes then the current to the third thyristor.
Then button 4 passes the current to the Latching relay's specific coil for ON state.
So to switch ON you need to hit the 724 buttons with the right sequence only!
If a wrong button is pushed in between the code will reset everything.
Buttons 1, 5, 9 and 3 are reset buttons. These buttons just resets the entry. Are there to only confuse the thief.
In practice you can remove 3 of them and use only one of these 4 buttons.
Button 8 change switch to OFF state
Button 6 is the "hold to use" button. This is the power on for the hole codding system.
This is the reason for stating "Zero consumption" at the title. Button 6 gives power to DC/DC converter to power the switching circuit.
So no power at all is being used for either ON or OFF state,
nor the controller consume anything as is completely disconnected from power.
So you need this button (6) to be always pressed before you enter the switch ON or the switch OFF code.
So to conclude codding:
Switch ON code: By Holding 6 enter 724
Switch OFF code: By Holding 6 enter 8
If coding does the oposite than the wanted, just swap the 1 and 2 terminals of the relay.
For the OFF state you need something fast and quick, so only one button is being used.
But with the demand of the holding 6 button makes a good protection from accidental pressing the 8 button.
You can place more thyristors and buttons to make the ON code longer etc.
The Particular relay is small light and powerful. It has two coils and not one.
It needs no power to hold the state as it uses magnets internally.
If you have a single coil latching relay available, then you need to alter the circuit to be use it.
For Relay HFE10-2-12-HT-L2 supplier : Click here
For the DC/DC down converter supplier : Click here
Enjoy your rides and your new cool switch ;)
FastNik Jan 7, 2022