Solid State Flasher for LEDs

The flasher unit (that thing for turn signals and hazard lights) stopped working today. The issue is that I switched to LEDs for the signal lights. These draw much less current than the original incandescent bulbs. When a regular bulb has failed, the flasher unit detects the lower current draw and speeds up the flasher. This is to indicate to the the driver that a bulb is not working. This was the situation ever since I switched to LED bulbs, and it may have contributed to the flasher's failure.



After opening it up, and pricing a replacement, I decided to make a new one. I chose to use the venerable 555 driving two small transistors in parallel to switch the lights.

I made the PCB to solder directly on the base of the failed flasher unit, which I de-soldered from the original PCB. Sometimes the first time is the charm - it worked when installed.








It makes no noise (the clicking was the relay in the original flasher) and it was a little strange at first. Of course, the really odd thing is that LR put the turn signal lever on the left of the steering column - on a right hand drive vehicle!

Current Monitor for 12V battery

A rather unpleasant discovery yesterday: the car refused to 'start.' Just like a typical ICE, the car uses the 12V battery to initiate the start up, closing the relays and main contactor, which connects the main pack to the motor controller and the DC-DC converter.

But if the 12V battery is dead, then the whole thing won't start.

Why did I do it this way? It seemed simpler at first. The original 12V was already in place, and there was even space for a second one on the other side of the car. (Not enough space for one of the pack batteries - physically too big!)

Plus, I am running the battery monitor and vehicle interface 24/7 off this battery. Which is the problem. The drain (I now know) is about 550mA. This adds up! if this was drawn from the battery in an ICE car, it would die too, as the charging from short trips is not enough to replace the energy used to start the engine and the 24/7 drain.

What to do? First get a handle on the currents into and out of the battery. I had seen this post a long time ago and thought it a pretty neat creation. So I designed one with two sensors, one for the current in from the DC-DC, the other for current out to the car.

The sensors are Allegro ACS756 which make use of the hall effect and have 3kV of isolation (nice but not necessary in this application.)

For electrical integrity, the terminals have some 14ga copper wire soldered around the pads.

For physical integrity, the whole board is through bolted to a alsab of 6mm teflon from a small kitchen cutting board.

The cpu used is an Atmel ATtiny45 in a DIP. I think these things are awesome: for about $1 there are 4 analog inputs and 2 GPIOs. It reads each current sensor, and sends the data out in a PWM code to the vehicle interface (an Atmel ATMega168)

Thus I learned that those 24/7 loads are between 0.5 and 0.6 amps.

Steering Wheel Repair

As long as I had the car, the turn signals would not turn off automatically when the wheel was rotated. At first, I thought this was a Land Rover 'feature,' but checking with a friend I determined that my vehicle was misbehaving.
I set out to understand how it should work. When a signal is activated, a small plastic rectangle is pushed toward the center of the steering column. This rectangle is in the same plane as a notched plastic disk which rides on the column. The steering wheel engages this disk with a slotted sleeve. On my car, this sleeve was plastic and it was broken.

Checking on ebay, I found other steering wheels with a cast aluminum sleeve, but these had airbags and/or radio controls on them as well. So I designed a replacement to be machined from steel or aluminum.



The lowest price I was quoted was $30, which is not unreasonable for the time involved, despite the simple design. But for that price I could buy a used steering wheel if I was willing to wait for shipping. Instead, I decided to make one myself from steel sheet.




Here it is mounted on the steering wheel. It is not pretty but it works.