Designing a simple bicycle turn signal circuit - need some help figuring out what the circuit needs

Thread Starter

acsdog

Joined Jun 1, 2018
7
Since I'm not currently taking classes and have some free time to kill, I've decided to design a simple turn indicator for the eBike I'm soon to buy. I have some experience in designing an electronic system for my school's robotics club, but most of what I did was simply making the circuit in Altium; my team lead did the higher-level design.

I have decided on the following requirements for the system:

Requirements:
  • On/off switch
  • Two signal buttons; one for left, one for right
  • 50% duty cycle on lights, with ~370 ms period
  • High-contrast indicators easily visible in daylight
  • Front and back indicators
  • Waterproof remote and indicators
  • Ability to unplug indicators from remote
  • Easily removable from bike
...that's about as far as I've gotten :/

To power the system, I'm thinking about using a 9V battery. That way I can step down the voltage and not worry about the battery's voltage curve going too low.

In order to make the blinkers visible in daylight, I'm thinking about using 10 or so for each blinker, so 40 in total (plus 2 on the remote so I don't leave my blinkers on like a fool :p). Assuming ~20 ma for each LED, that's at least 840 ma of current, plus whatever the other components will use. I'm not sure if a standard 9V can support that. If it can't, or if that would kill the battery very quickly, I could use some suggestions for batteries.

To control the frequency of the blinking I'm thinking about using a 555 timer. Since the timer can't have ~840 ma of current running through it, I'll use a photocoupler to isolate the timer from the indicators. This also protects the circuit in case the blinkers short out (likely, given the abundance of water in Florida).

In my experience with Arduino circuits, tactile pushbutton switches run into an issue known as 'bounce', so I'll have to implement a debouncing circuit lest my blinkers rapidly switch on and off when I press the button.

To regulate the voltage, I did some research and it looks like a zener diode is a good option. If the battery voltage drops too low, the zener diode should prevent the circuit from receiving inadequate voltage.

I'll need to find waterproof connectors for connecting the blinkers to the remote. I know I'll never make it 100% waterproof, but it needs to withstand the rain.

Finally, I'll need some sort of fuse. I don't think a physical fuse is necessary for this low a current, but I'm not sure what else to use.



That about sums it up. Is my circuit missing any crucial parts? I know there will be additional components per the datasheets for the timer and whatnot, but if I'm missing anything big, please let me know.

Thanks!
 

MrChips

Joined Oct 2, 2009
19,280
Welcome to AAC!
Nice idea but you are on the wrong path in many respects.

1) a PP3 9V battery is a very poor choice. You will be lucky to get 500mAh, i.e. 50mA for 10 hours.

2) A 555-timer is ok since it can switch 200mA. You do not need optocouplers.

3) There is no need to debounce your switches unless you are planning to have a push-on/push-off function.

4) Zener diodes are energy hogs. Hence they counteract your desire for energy efficiency.

5) You ought to be looking at rechargreable 18560 Li-ion batteries which can deliver 3.6V @ 5000mA.
 

Thread Starter

acsdog

Joined Jun 1, 2018
7
Welcome to AAC!
Nice idea but you are on the wrong path in many respects.

1) a PP3 9V battery is a very poor choice. You will be lucky to get 500mAh, i.e. 50mA for 10 hours.

2) A 555-timer is ok since it can switch 200mA. You do not need optocouplers.

3) There is no need to debounce your switches unless you are planning to have a push-on/push-off function.

4) Zener diodes are energy hogs. Hence they counteract your desire for energy efficiency.

5) You ought to be looking at rechargreable 18560 Li-ion batteries which can deliver 3.6V @ 5000mA.
Thanks for the quick response!

I figured a standard 9V battery probably wouldn't suffice, but didn't know what else to look at. I'll look into Li-ion batteries.

As for the optocoupler, I'd still like to have it for short protection reasons. The ones I'm looking at also have ratings of up to around 200mA, but my LEDs will probably draw more than that.

The blinkers will be toggled on or off with 2 buttons (1 for left, 1 for right), so I will probably need to debounce.

As for voltage regulation, what do you suggest I use that's lightweight and cheap? If i'm going to be using Li-ion, I need to be extra careful not to completely discharge, so I'll need a voltage cutoff when the battery gets too low.
 

KJ6EAD

Joined Apr 30, 2011
1,568
Have you looked at what may exist commercially as a starting point for design?

Most of the electronics needed will be trivial or available off the shelf but your mechanical requirements of water resistance and mounting will probably be challenging.

If you were to buy commercial truck clearance lights, you'd have a waterproof light in a robust housing known to be daylight visible. You'd only need to supply 12V, some mounting hardware and your control system.
 
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Thread Starter

acsdog

Joined Jun 1, 2018
7
Have you looked at what may exist commercially as a starting point for design?

Most of the electronics needed will be trivial or available off the shelf but your mechanical requirements of water resistance and mounting will probably be challenging.

If you were to buy commercial truck clearance lights, you'd have a waterproof light in a robust housing known to be daylight visible. You'd only need to supply 12V, some mounting hardware and your control system.
Good idea! I did some looking and found some for $5 a piece.

As for the mounting, I work at a bicycle shop and can probably use an old discarded mount and 3D print an adapter. Or just JB weld it lol. I can get a waterproof electronics case for the circuit, but the challenge will be waterproofing the buttons. A reed switch with magnetic buttons could solve this.
 

KJ6EAD

Joined Apr 30, 2011
1,568
There are plenty of industrial and marine switches that are waterproof and will seal to a panel but they tend to be expensive and bulky. There may be a compression molded button panel with the directional arrows and one or two additional buttons you need like the ones used on existing bicycle turn signal products.
 
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Thread Starter

acsdog

Joined Jun 1, 2018
7
Welcome to AAC!
Nice idea but you are on the wrong path in many respects.

1) a PP3 9V battery is a very poor choice. You will be lucky to get 500mAh, i.e. 50mA for 10 hours.

2) A 555-timer is ok since it can switch 200mA. You do not need optocouplers.

3) There is no need to debounce your switches unless you are planning to have a push-on/push-off function.

4) Zener diodes are energy hogs. Hence they counteract your desire for energy efficiency.

5) You ought to be looking at rechargreable 18560 Li-ion batteries which can deliver 3.6V @ 5000mA.
I found a pack of 10 12v truck indicator lights. Waterproof, bright, and cheap. How do I increase the voltage to power these with a 3.6V or 12V battery? Will I need to worry about over-discharging the battery if it has built-in protection circuitry?
 

Thread Starter

acsdog

Joined Jun 1, 2018
7
12V penny lights take 20mA and are very bright. All you need is a 555-timer and a 12V battery.

Ended up getting a pack of 10 of these lights. My 555 timers and other components came in, and I got a working circuit on my breadboard! Just waiting on my battery, wire, and epoxy so I can build the box.

Only problem I have with the circuit is that the blinking rate changes noticeably with temperature. If I touch either of the timing resistors, it can increase by 2-3 Hz. No big deal, it still does what it needs to do. I could always get some low TC components if I wanted a more stable output.Bike Blinker.PNG
 

Thread Starter

acsdog

Joined Jun 1, 2018
7
Are you using NE555? Try using CMOS versions of 555-timer instead, such as LMC555 or TLC555.
What would be the benefit of that? Less power consumption?

The battery I'm using is 3000 mAh, which is more than enough for 4 LEDs. I will be using a DPDT switch to switch both the timer and one of the LED sides, that way the timer isn't constantly running.
 

MrChips

Joined Oct 2, 2009
19,280
What would be the benefit of that? Less power consumption?

The battery I'm using is 3000 mAh, which is more than enough for 4 LEDs. I will be using a DPDT switch to switch both the timer and one of the LED sides, that way the timer isn't constantly running.
The benefit could be less temperature dependency considering that R2 is 1MΩ which is rather high of TTL circuitry.

Edit: Sorry, I retract what I wrote. I see in the LM555 spec sheet the chart uses a 10MΩ resistor.
 

AnalogKid

Joined Aug 1, 2013
8,109
Since you are not worried about generating megahertz RF interference with a switching power supply, you can delete R3.

Increase R1 to 10K. It will have negligible impact on the duty cycle, and will reduce the power dissipation in the discharge transistor by 90%. This also will let pin 7 present a lower impedance to R2, which might help with the frequency stability a small amount. For better 50/50 performance with one fewer resistor, change to the "other" 555 astable circuit, which uses the output pin 3 to drive the timing network:



By design, the frequency stability of a 555 astable circuit is almost entirely dependent on the external components. Consider NP0 or C0G capacitor types, maybe multiple pieces in parallel. In the US, 1% and 0.1% resistors are pretty cheap. You don't need that kind of accuracy, but they come with better tempco's.

ak
 
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