Motorcycle Flasher Circuit validation

[Joe_echo]

Evening all,

Would you kind people be able to pick over my design and let me know if there are any issues you can foresee.

I have a motorcycle that has been badly wired with all cables and wire taps over the place. I am integrating a single 12-14V DC supply from the battery into a PCB and having it feed the lighting circuits through the handle bar switchgear.

As part of this I have designed the attached Flasher circuit to supply the LED indicators, these draw around 1W front and rear. So 2W per side and grounded through the indicator itself. The indicator switch on the handle bar feeds the flasher output to the LED, so high side switching is required.

I have a 555 timer set to 50% duty cycle and a frequency of 1.5Hz, the output of which goes to the base on a PNP transistor, when the 555 is high the PNP doesn't conduct, when low the PNP is in saturation. Please ignore the Cap and resistor values in the schematic, they are just for the pcb design footprints.

The actual values are as follows.

R1 = 10K
R2 = 100K
R3 = 1K
R4 = 5.1K
C1 = 47uF
C2 = 100nF

Would there be an issue with the collector of the PNP effectively being floating unless the indicators are on and grounded?

[bson]

Because of the gate pullup resistor the 12V supply will never float if switched off.

The easiest solution would be to power your turn signal circuit from the same 12V switched supply, so if it's not used it's not powered.

Is 12V from the battery terminals or rectifier/regulator?  If so, be aware it's going to be more like 11-14.6V with nasty transients, and not very kind to small-signal components.

[Joe_echo]

The supply is from the battery not the regulator/rectifer. If needed I can protect from transients with a zener.

The 12v switched is the power supply rail from a NO relay that is switched using the ignition, thus when the bike isn't running the entire board is powered down.

Hopefully the below makes a little more sense. The relay output will also have the horn and a auxillary dash on it.

[moffy]

You might want to drop the value of R3 just to ensure that the 2N2907 saturates fully.

[Joe_echo]

Will do, will likely drop it to around 700 Ohm which will give around 15mA of base current.

[Benta]

It's missing the "blown bulb fast flashing", which is mandatory for getting your bike approved.

[Joe_echo]

As far as I am aware its not mandatory in the UK especially for a bike that didn't come with Indicators in the first place.

[themadhippy]

might want to add an annoying buzzer as a reminder you've flipped the indicator

[Benta]

As far as I am aware its not mandatory in the UK especially for a bike that didn't come with Indicators in the first place.

As no one knows what bike it is, you're probably right.

[DavidKo]

If the motorbike is used on the roads, than type approval need to be done. Same think is valid for anything what you add. Like addition high beam reflectors, daytime running light, position lamps etc. Regulations do not care if it was there in the first place (you can omit some devices for specific use cases), if it is mounted than you need to comply with regulations.

[SteveThackery]

might want to add an annoying buzzer as a reminder you've flipped the indicator

Yes. As a motorcyclist myself I know how easy it is to leave the indicators on. As a result, I would use a little microcontroller for this job. It might sound over the top, but it makes it easy to respond to various conditions. A current sensor will let you know whether two, one, or no LED lamps are flashing, and you can adjust the flash speed accordingly; you can control the tell-tale bulb separately, so for example if one lamp is faulty, you could flash the other at the normal speed but double-time the tell-tale so you know there's a problem. Finally, you could sound a buzzer if the indicators have been on an unfeasible amount of time.

All of this is trivial to implement on a microcontroller, but would add quite some complexity in normal hardware.

[SteveThackery]

If the motorbike is used on the roads, than type approval need to be done. Same think is valid for anything what you add. Like addition high beam reflectors, daytime running light, position lamps etc. Regulations do not care if it was there in the first place (you can omit some devices for specific use cases), if it is mounted than you need to comply with regulations.

I'm sure this is true, but there's no chance whatever of being found out. When it goes for its annual MOT test, the tester will check that all the indicators - and the tell-tale - flash at the correct rate. That's it. No checking is done on what happens when a lamp is disconnected.

[Joe_echo]

The bike is a Honda CRF450X trail bike. Currently the indicators are controlled using a flasher relay.

In the UK Type Approval would be an MOT test. The test is only to ensure that the items attached work within the limited requirements. For example the Indicators must flash between 1 and 2 Hz.

I'm not concerned about a buzzer as it would have to be fairly loud to be heard over the noise of the exhaust.

[SteveThackery]

So why do you want to use a home brew flasher anyway? Every other bike on the road uses an off-the-shelf flasher relay. Wouldn't that be easier?

[themadhippy]

I would use a little microcontroller for this job. It might sound over the top,

yep certainly ott,my method was a bridge rectifier across the repeater  light.But that was back in the days ya could buy 2 stroke mix at the petrol station.

[Joe_echo]

I am integrating the mass of wiring jammed behind the headlight into PCB and adding waterproof connectors so wanted to add the flasher to the pcb. The previous owner did a number on the wiring and it goes on the fritz when it gets mildly damp. Not great for an offroad bike.

Also I enjoy trying to improve things.

[SteveThackery]

Also I enjoy trying to improve things.

Me too. In fact I made a flasher circuit very like I described above. But there's no way a home brew 555 circuit is an improvement over an off-the-shelf three-terminal flasher relay. Your talents are wasted on it.

[SteveThackery]

I would use a little microcontroller for this job. It might sound over the top,

yep certainly ott,my method was a bridge rectifier across the repeater  light.

Your method to do what? The OP wants to incorporate a home brew flasher circuit into a PCB with other functions. Personally I think he should simply incorporate a relay socket onto the PCB and use a standard LED-capable flasher relay, available dirt cheap from everywhere.

As an aside, I've done the same as you: put a bridge rectifier across the repeater light and used it to power a PIC, which counts the number of flashes and then starts beeping as a reminder to cancel the indicators. It worked great.

[djsb]

You will have more problems in the harsh conditions encountered on a motorcycle (condensation,corrosion,vibration, electrical noise/transients) than simply using standard parts. This company sells a lot of what you need.

https://www.vehiclewiringproducts.co.uk/c-82-motorcycle-parts

You could also try wemoto or David Silver spares.

I have 2 motorcycles (Honda NC750X and Royal Enfield Himalayan 411) and I've bought parts from the above three companies before.
It will be enough of a task trying to figure out the poor wiring.

[SteveThackery]

You will have more problems in the harsh conditions encountered on a motorcycle (condensation,corrosion,vibration, electrical noise/transients) than simply using standard parts. This company sells a lot of what you need.

I completely disagree, and that disagreement is based on significant experience. Yes, good quality connectors are important, especially if they are exposed. Beyond that, bog standard components on bog standard PCBs or Veroboard work fine. All it needs is a modicum of common sense. For example, when I've finalised the circuit I spray it with conformal coating. Also, I box up the circuit and then fasten the box to the bike with hook-and-loop strip, which is brilliant at absorbing vibration. Inputs and outputs have diode protection.

As I say, it's all trivial and common sense. And I've never had any of my motorcycle electronics fail.

[floobydust]

I've repaired many motorcycle electronic modules and the main killer is vibration and water, bad connections, followed by dirty power then heat killing semi's. Some are just a weak design. Of course it depends on the bike, but generally a naked 16V IC will not last here.

OP I don't think you will have much success with your circuit. I'd recommend breadboarding it first before making a PCB.
Your circuit and your part value ref. designators don't agree.
Timing cap C2 gets charged and discharged via R1. R2 is in the way. V_OH for a 555 is not so great, to fully turn off the 2907.
You must have some power filtering and transient protection. Don't forget something to act as a fuse if a lamp (socket) shorts, at least cover the IC.
What kind of lamps are these? Q1 is very small.
NE555 datasheet

[themadhippy]

Your method to do what?

making a buzzer buzz with the blinking lights

I completely disagree, and that disagreement is based on significant experience

I disagree with your disagreement. The bike i had the biggest electrical problems with was also the one that had  lots of electrickery gimmickery,like the  fuel reserve switch on the bars instead of an ole skool  tap down by your knees ,that didnt last a year before the electronic valve packed up,the self canceling indicators that would self cancel with in a millisecond of being turned on or the alarm that you could jump on the bike or push it down the road in perfect peace but  a slight puff of wind came in  the wrong direction and off it went,the final straw was the neutral interlock becoming permanently interlocked  and  the bike refusing to start.All of that in less than 2 years  from new. Pity there bike division didn't get reliability   lessons from there pro audio side

the mass of wiring jammed behind the headlight

just like every bike ive owned,its an ideal empty container in an ideal location complete with built in heating.

[Zero999]

The problem is there can be high voltage transients on the 12V system, for example during load dump, when the battery becomes disconnected from the alternator, which causes its output to spike above 100V. This is more of an issue on motorcycles, especially the older ones, than cars. Unfortunately it'll smoke a 555 timer. Off the shelf flasher circuits are protected against high voltages.

If I had to design an astable to flash an LED from a 12V system, I would use semiconductors rated to 120V or more and go with the old two transistor astable.

Here's an example, which should be able to stand 120V for 400ms, so long as the resistors and LEDs can take the surges.

[Zero999]

It's missing the "blown bulb fast flashing", which is mandatory for getting your bike approved.

How about a speaker connected in series with a capacitor across the output? If the lamp fails, then the capacitor will just charge up and it will only click once the capacitor charges up, because there won't be anything to discharge it. I accept it's impractical on a motorcycle and isn't needed here, but I thought I'm mention it anyway.

[Joe_echo]

The mass of wiring has now been sorted out and traced to the various circuits, so I know what goes where. With regards to components, I have a large number of JST waterproof connectors and a few Deutsch left from other projects. The PCB will be located in a 3d printed housing tucked up behind the front headlight. Components will be SMD and those that aren't will be siliconed to the board to help with the vibration.

I have added a TVS to the main supply to protect against transients and upgraded the 555 to a 7555 cmos chip. Lighting is all LED so a small draw on the system, the indicators draw 160mA each.

Worst case it doesn't work and I've learnt something.