Replacing Broken Car Speakers

Some Cars are Old

Recently, I bought a very used car in the hopes of modifying it to use a parallel-hybrid drivetrain. I’d like to cut the driveshaft and slot an electric motor inline with it, and that will probably be the subject of future posts if I can find a garage willing to do most of the heavy lifting and cutting.

But in the meantime, what sort of car do you get if you’re thinking of cutting its driveshaft in half? A cheap one, of course – and my choices were further limited by a few basic requirements:

The car should actually be a small pickup truck; the bed is an ideal place to put the heavy batteries, they tend to have a lot of ground clearance for fitting a bulky motor underneath the chassis which means little or no changes to the bodywork, and passenger space is not a consideration in this build.
It should be rear-wheel drive. Since I am planning to add a motor between the transmission and the differential, there needs to be enough space along the driveshaft to fit the motor. That means either rear-wheel drive with the engine in the front, or front-wheel drive with the engine in the back. And I don’t know of any rear-engine pickup trucks.
It should have an automatic transmission. This kind of simple conversion leaves you with two acceleration pedals, and I don’t have enough feet to use four pedals at once.

So I wound up with a cheap-and-cheerful 1994 Toyota Pickup Truck. It doesn’t actually have a model name; in North America, the Hilux brand was renamed to “Truck” in the 1970s before eventually being replaced with the Tacoma. So this is not a luxury vehicle. It has roll-up windows, it does not have ABS, it came with a broken speedometer, and more importantly its speakers had disintegrated in the decades since 1994.

Yikes.

That’s no good, and it sounded like the buzzing of a thousand wasps. Plus, replacing your speakers seems like a pretty easy first project if you want to learn about a car. You only have to remove a few interior panels, and your sound system is a safe thing to break compared to say, your brakes. So let’s get started! These specific instructions may be for a 1994 Toyota pickup, but I’ll bet the process looks similar for the front speakers of other cars.

Preparation

When you realize that your speakers are broken, one of the first things you should do is get some new speakers. It turns out that they come in several different sizes though, and you’ll need to get the right size for your vehicle. If you’re buying new ones, most car stereo stores will probably be happy to look up what sizes will fit your make/model. Or, it looks like a company called Sonic Electronix has a glossary that you can check. For a 1994 Toyota Pickup, they recommend 4″ speakers in the front and 6.75″ speakers in the side panels. But the truck I picked up does not have a rear seat, so there are no speakers in the side panels and I only needed a pair of 4″ ones.

I picked up some fairly cheap ones since I didn’t want to spend too much, I’m not exactly an audiophile, and I’m not sure how much power this truck can spend on audio since the stock speakers were only 15W each. And as long as the new ones were intact, they’d be an improvement.

With a working pair of speakers in hand, it’s time to remove the broken ones and swap in the new ones. Our first stop will be the vehicle’s service manual – with any luck, your car will have some sort of repair, maintenance, or service manual available online which will have a lot more information than the owner’s manual in your glove box. There are a couple of resources available for an early ’90s Toyota Pickup, such as this helpful site. There are also FTP mirrors that you can scrape for offline reference, if you are so inclined:

wget -r --no-parent -A ".pdf" http://htftp.offroadsz.com/marinhaker/programi/toyota/

So a big thank you to Marin for that.

Replacing the Old Speakers

Looking at the ‘Body (Mechanical) / Instrumentation’ section, we can see that removing the panels is as simple as removing a few screws and bolts. I wound up using a medium-sized philips-head screwdriver and a 10mm hex driver:

The panels with speakers behind them are the ‘Lower Finish Panels’ No. 1 and 2.

Passenger Side

Starting on the passenger side, there are 4 screws and 1 bolt holding the glove box onto the dashboard, and the speaker is located right next to the glove box. After unscrewing it, the whole panel should pop out after a bit of finagling. You might have to reach behind the plastic lips and un-hook some corners. Or who knows, your vehicle might have its panels assembled in a completely different way. But here, the assembly comes out fairly easily and its only other connection to the rest of the car is the speaker’s wiring.

The glove box, outside of its natural habitat

The audio connectors in this car are simple clip-on plugs. And as luck would have it, they also connect to the speakers with the same ‘spade’ terminals that my new speakers used. I guess that’s probably standardized, if the plugs haven’t changed in ~25 years. This is hard to mess up; one terminal/plug pair is wider than the other, so there’s only one way that the wiring will easily fit.

Once you unscrew the old speaker to remove it from the panel, it’s worth salvaging the connector to avoid soldering or splicing wires together. Unfortunately, these speakers were assembled in a way that made it almost impossible to cleanly remove the connectors; they were glued together such that each connector covered the screw which held it in place. If you run into that sort of problem, carefully applying a crowbar worked for me.

Close enough.

If your speakers are dead like mine were, they’re basically junk at this point. We ended up chiseling the big magnets off and sanding them down to make large magnetic part trays, but you could just toss them in the recycling bin too. Next, just screw the new speakers in place and connect them to your stereo with the salvaged plug.

The old connector plugs right onto the new speaker’s spade terminals.

Before you screw the panel back on, check that the speaker sounds okay by turning your stereo on and listening to it.

Driver Side

The process for replacing the driver-side speaker is pretty much the same – you just have to remove a different panel. Looking back to the service manual, the driver-side panel also has 4 screws and 1 bolt holding it on. In my case, it was also necessary to unscrew the lever which opens the hood, which is shown on a different page:

Don’t forget to remove the hood catch, if it’s attached to the panel you’re removing.

The plastic housing around the keyhole also popped off when I pulled the panel out, but it pops back in too. Once the driver-side panel is removed, it’s the same process of removing the old speaker, salvaging its connector, screwing the new speaker in, and re-connecting it with the old plug. Test the speaker before re-attaching the panel, and don’t forget to re-attach the hood catch lever.

Conclusions

That’s all there is to it – I guess that speakers are probably one of the easiest thing to change on a car, especially when you’re not also replacing the stereo. And this might not have made a huge difference if the speakers weren’t already shot – there are still only two small speakers connected to a ’90s radio with a cassette player. Still, it’s a fun and simple way to learn a little more about your car, and you’re not very likely to break anything expensive compared to other modifications that you might want to make.

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Simple USB / Serial Communication with the CP2102N

Several years ago, a company called Future Technology Devices International (FTDI) sold what may have been the most popular USB / Serial converter on the market at the time, called the FT232R. But this post is not about the FT232R, because that chip is now known for its sordid history. Year after year, FTDI enjoyed their successful chip’s market position – some would say that they rested too long on their laurels without innovating or reducing prices. Eventually, small microcontrollers advanced to the point where it was possible to program a cheap MCU to identify itself as an FT232R chip and do the same work, so a number of manufacturers with questionable ethics did just that. FTDI took issue with the blatant counterfeiting, but they were unable to resolve their dispute through the legal system to their satisfaction, possibly because most of the counterfeiters were overseas and difficult to definitively trace down. Eventually, they had the bright idea of publishing a driver update which caused the counterfeit chips to stop working when they were plugged into a machine with the newest drivers.

FTDI may have technically been within their rights to do that, but it turned out to be a mistake as far as the market was concerned – as a business case study, this shows why you should not target your customers in retaliation for the actions of a 3rd party. Not many of FTDI’s customers were aware that they had counterfeit chips in their supply lines – many companies don’t even do their own purchasing of individual components – so companies around the world started to get unexpected angry calls from customers whose toy/media device/etc mysteriously stopped working after being plugged into a Windows machine. You might say that this (and the ensuing returns) left a bad taste in their mouths, so while FTDI has since recanted, a large vacuum opened up in the USB / Serial converter market almost overnight.

Okay, that might be a bit of a dramatized and biased take, but I don’t like it when companies abuse their market positions. Chips like the CH340 and CH330 were already entering the low end of the market with ultra-affordable and easy-to-assemble solutions, but I haven’t seen them much outside of Chinese boards, possibly due to a lack of multilingual documentation or availability from Western distributors. So at least in the US, the most popular successor to the FT232R seems to have been Silicon Labs’ CP2102N.

It’s nice to have a cheap-and-cheerful way to put a USB plug which speaks UART onto your microcontroller boards, so in this post, I’ll review how to make a simple USB / UART converter using the CP2102N. The chip comes in 20-, 24-, and 28-pin variants – I’ll use the 24-pin one because it’s smaller than the 28-pin one and the 20-pin one looks like it has some weird corner pads that might be hard to solder. We’ll end up with a simple, small board that you can plug into a USB port to talk UART:

Drivers for the CP2102N are included in most popular OSes these days, including Linux distributions, so it’s mostly plug-and-play.

It’s worth noting that you can buy minimal CP2102N boards from AliExpress or TaoBao for about $1, but where’s the fun in that?

New 8-pin ARM Core: the STM32G031J6

It has been about nine months since ST released their new STM32G0 line of microcontrollers to ordinary people like us, and recently they released some new chips in the same linup. It sounds like ST wants this new line of chips to compete with smaller 8-bit micros such as Microchip’s venerable AVR cores, and for that market, their first round of STM32G071xB chips might be too expensive and/or too difficult to assemble on circuit boards with low dimensional tolerances.

Previously, your best bet for an STM32 to run a low-cost / low-complexity application was probably one of the cheaper STM32F0 or STM32L0 chips, which are offered in 16- and 20-pin TSSOP packages with pins spaced 0.65mm apart. They work great, but they can be difficult to use for rapid prototyping. It’s hard to mill or etch your own circuit board with tight enough tolerances, and it’s not very easy to solder the chips by hand. Plus, the aging STM32F031F6 still costs $0.80 each at quantities of more than 10,000 or so, and that’s pretty expensive for the ultra-cheap microcontroller market.

Pinout and minimal circuit for an STM32G031J6 – you only really need one capacitor if you have a stable 3.3V source.

Enter the STM32G031J6: an STM32 chip which comes in a standard SOIC-8 package with 32KB Flash, 8KB RAM, a 64MHz speed limit, and a $0.60 bulk price tag (closer to $1.20-1.40 each if you’re only buying a few). That all compares favorably to small 8-pin AVR chips, and it looks like they might also use a bit less power at the same clock speeds. Power consumption is a tricky topic because it can vary a lot depending on things like how your application uses the chip’s peripherals or what voltage the chip runs off of. But the STM32G0 series claims to use less than 100uA/MHz, and that is significantly less than the 300uA/MHz indicated in the ATTiny datasheets. Also, these are 32-bit chips, so they have a larger address space and they can process more data per instruction than an 8-bit chip can.

Considering how easy STM32 chips are to work with, it seems like a no-brainer, right? So let’s see how easy it is to get set up with one of these chips and blink an LED.

Mounting Solar Panels to a Car

As someone who likes both electronics and the outdoors, sometimes I get anxiety about a lack of electricity. It would be nice to go camping somewhere away from it all, and still be able to charge things and run some lights, a display, maybe a small cooler. I’m sure some of you are rolling your eyes at that, but I’ve also been wanting to play with adding aftermarket indicators to old cars, like backup sensors or blind spot warnings, and it’d be nice to run them off a separate battery to avoid the possibility of accidentally draining the car’s battery overnight.

Since low-power solar panels are fairly cheap these days, I figured that it might be worth buying a few to mount to my car’s roof. And since my car is technically a pickup, it was very easy to put the battery in the bed and run the wiring through the canopy’s front window:

Picture of the solar system's general setup

I’ve secured the battery a bit more since taking these pictures, but this is the basic idea – it’s pretty simple.

If you have a different kind of car, I’d imagine that you could just as easily put the battery in your trunk, but you might need to drill a hole for the wires if you don’t want to leave one of your windows cracked open.

I guess that a lot of this guide won’t apply exactly to your situation, because you’ll have different dimensions to work with, different limitations, and probably different solar panels. But I hope that laying out each step that I took and what worked for me might be helpful – your basic approach could probably look very similar.

And before we go any further, please keep your expectations in check. These panels can only produce up to 100W in direct sunlight, which is nowhere near enough power for something like an electric vehicle. So read on if this sounds interesting, but the car still runs on gas. We’re not saving the world here.