Redlining Your CPU via Automotive Tachometer

Many CPU-usage widgets have stylistically borrowed from vehicles, displaying something mimicking the tachometer found in the dashboard. [Pat] took it a step further and tried his hand at re-borrowing this style. He figured, why not use an actual physical tachometer to display how hard the CPU on his Raspberry Pi was revving?

With the goal of tuning 0-100% CPU usage to 0-8000 RPM on the tach, the first step was diagnosing the range of PWM input frequencies that moved the needle across the tach’s full arc. Using his Tektronix 3252C function generator he quickly determined 0-440 Hz would be needed and graphed a handful of intermediate points. The response curve was not linear, so he drew up some fudging guidelines to make all the datapoints match.

Next, he wrote a few lines of Python (he shared) to make the Pi to poll its CPU usage and translate it to the proper frequency. The Pi makes outputting easy, GPIO pin 11 carried the signal to a 7404 for buffering, then out to the tach. The automotive tach itself ran on 12V, but its input signal required only 5V so he pulled a 7805 from his parts bin.

Once it was all put together it worked beautifully using just the one extra component. Some might see this as more clever than USB dependent or Arduino bloated based tachometer hacks.

See the video after the break of the tach twitching even when the mouse moved, and pegging the red when opening a browser. No more need to use up valuable screen real-estate (or use a screen at all) if you want to see at a glance when your Pi is putting in work.

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$15 Car Stereo Bluetooth Upgrade

We’ve seen all sorts of ways to implement Bluetooth connectivity on your car stereo, but [Tony’s] hack may be the cheapest and easiest way yet. The above-featured Bluetooth receiver is a measly $15 over at Amazon (actually $7.50 today—it’s Cyber Monday after all) and couldn’t be any more hacker-friendly. It features a headphone jack for plugging into your car’s AUX port and is powered via USB.

[Tony] didn’t want the receiver clunking around in the console, though, so he cracked it open and went about integrating it directly by soldering the appropriate USB pins to 5V and GND on the stereo. There was just one catch: the stereo had no AUX input. [Tony] needed to rig his own, so he hijacked the CD player’s left and right audio channels (read about it in his other post), which he then soldered to the audio output of the Bluetooth device. After shoving all the bits back into the dashboard, [Tony] just needed to fool his stereo into thinking a CD was playing, so he burned a disc with 10 hours of silence to spin while the tunes play wirelessly. Nice!

An Interview with Tesla Battery Hacker [wk057]

We covered [wk057] and his Tesla Model S battery teardown back in September. Since then we had some time to catch up with him, and ask a few questions.

You’ve mentioned that you have a (non hacked) Tesla Model S. What do you think of the car?

It’s the best car I’ve ever driven or owned, period. Not to get too into it, but, I love it. I’ve put almost 20,000 miles on it already in under a year and I have no real complaints. Software feature requests… but no complaints. After almost a year, multiple 1700-miles-in-a-weekend trips, and an overall great experience… I can never go back to a gas vehicle after this. It would be like going back to horses and buggies.

A salvage Tesla Lithium battery had to be expensive compared to a Lead Acid setup. What made you go with the Tesla?

Actually, if you consider that the Model S battery is already pre-setup as a high-capacity pack, contains the wiring to do so, and the modules are much more energy and power dense than any lead acid battery bank, it’s actually almost cheaper than a comparable lead acid bank and all the trimmings.

I haven’t officially weighed them, but the modules from the Model S battery are roughly 80 lbs. 80 lbs for a 5.3 kWh battery is around 15 lbs per kWh, which is impressive. For comparison, a decent lead acid battery will have a little over 1 kWh (of low-rate discharge capacity) and weigh almost the same.

Also, the Tesla pack is much more powerful than a lead acid bank of the same capacity.
Generally a lead acid battery bank would have a capacity that would only be realized with slow discharges, so, 1/20C. Much over that and you sacrifice capacity for power. 1/20C for an 85kWh pack is only 4.25kW, barely enough for a central air unit and some lights without losing capacity.

Now the Tesla pack can be discharged (based on how it does so in the vehicle) at up to 3.75C for short periods, and at 1/2C continuously without really affecting the overall capacity of the pack. That means I can run 10x more power than lead acid without a loss in overall charge capacity. Leads to a much more flexible battery solution since the loads will, in reality, always be so low that this will not even come into play with the Tesla pack, but would almost always be a factor with lead acid.

Charging is also somewhat better with the Tesla battery. Charge a lead acid battery at a 1/2C and it will boil. Charge the Tesla pack at 1/2C (42kW) and it might warm up a few degrees. Oh, and the charging losses at high rates are much less than lead acid also.
Overall, without continuing to yack about the technical aspects, it’s just a much better battery, takes up less space, weighs less, and has more power available.

There are likely decent arguments for other solutions, but the rest aside, this one won out because it was definitely more interesting.

Click past the break to read the rest of our interview with [wk057]!

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Capacitive Garage Door Opener Hides Behind Your Dash

[Pyrow] wanted to upgrade his garage door opener remote. It worked just fine, but changing those tiny batteries out can be an inconvenience. Plus, the remote control was taking up valuable storage space and would always rattle around while driving. [Pyrow] decided to make use of an Omron E2K-F10MC2 capacitive touch sensor to fix these issues.

[Pyrow’s] circuit still makes use of the original remote control. He just added some of his own components to get it to do what he wanted. The circuit is powered by the car’s battery, so it never needs a battery replacement. The circuit is protected with a fuse and the power is regulated to prevent electrical spikes from burning up the original remote control. The actual circuit is pretty simple and uses mostly discrete components. It’s all soldered onto proto board to keep it together. He only had to solder to three places on the original remote control in order to provide power and simulate a button press.

Next, [Pyrow] took his dash apart. He used double-sided tape to attach the touch sensor to the back of the dash.  After securing the electronics in place with tape, he now has a working hidden garage door opener. Full schematics are available in the writeup linked above. Also, be sure to watch the demonstration video below.

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Destroy your Volkswagen Touch Adapter for Bluetooth’s Sake

[Mansour]’s Volkswagen Polo has a touch-screen adapter with voice recognition to control a bunch of the car’s features, but he wanted it gone.

Voice control of your car sounds like a great thing, right? Well, the touch adapter blocked other Bluetooth devices from connecting directly to the car, and prevented him from streaming music from his phone while he’s connecting it through the adapter. But if you simply throw the adapter away, the car won’t connect to any Bluetooth devices.

So what options are left? Other than a couple of expensive or complicated options, [Mansour] decided to open up the device and desolder the Bluetooth chip and antenna. Admittedly, it’s not the deepest hack in the world, but we’ve gotta give [Mansour] credit for taking the technology into his own hands.

Disabling unwanted functionality is not uncommon these days. Who hasn’t stuck tape over their laptop’s camera or kept an RFID card in a Faraday wallet? What other devices have you had to “break” in order to make them work for you?

Ceci N’est Pas Une Clock

[Justin] tipped us about his slick custom OBD-II gauge that could easily pass for an OEM module. He was able to use the clock area of his Subaru BRZ to display a bunch of information including the oil and coolant temperatures and the battery voltage.

The forum post linked above has a good FAQ-based explanation of what he did, but so many people have told him to shut up and take their money that he created an Instructable for it. Basically, he’s got a Sparkfun OBD-II UART board communicating with a pro Trinket. The display is an Adafruit OLED, which he found to be an ideal choice for all the various and sundry light conditions inside the average car.

[Justin] was able to reuse the (H)our and (M)inute buttons and reassigned them to (H)igh to show the peak reading and (M)ode to, well, switch between modes. The (:00) now resets the peak readings. He offers suggestions for acquiring the specific CAN codes for your car to make the data more meaningful. [Justin]’s code is safe in the many tentacles of Octocat, and you can check out his demo video below.

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A Mobile Radio Power Controller

[Pete], a.k.a. [KD8TBW] wanted to install his Yaesu radio in his car. From experience, he knew that having a radio in a car inevitable led to leaving it on once in a while, and this time, he wanted a device that would turn his rig on and off when the key was in the ignition. He ended up building a mobile radio power converter. It takes the 12V from the car when the alternator is running, and shuts everything off when the engine has stopped.

The Yaesu radio in question – an FT-8800 does have an automatic power off feature, but this is a terrible way of doing things. There is no way to turn the radio back on, and the radio must be left in a non-scanning mode.

In what he hopes to be his last design in EagleCAD, [Pete] whipped up a board featuring an ATtiny85 that measures the voltage in the car; when it’s ~14V, the alternator is working, and the radio can be switched on. When it drops to ~12V, it’s time to turn the radio off. It’s a great project, and with the 3D printed case, it can easily be shoved inside the console. Video below.

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