I despise these wheels. About 15 years ago, my wife and I went to Target and first went to lunch at the far end of the parking lot. After lunch we headed into the store, grabbed a cart, now loaded with our newborn in his car seat, and our two year old sitting in the cart. A quick shopping trip later, we headed back to the car. When crossing the Target parking lot, the wheels locked up, in the middle of the road. Cart wouldn’t budge. Traffic all over the place, and now I have to pull both my children out, along with the shopping, and carry them all to my car. Pissed is an understatement. After my wife and kids were secured back in the car, I retuned to Target, complaining to the manager. A shrug was the best I received. Why did they need to put the wire in the middle of the road???
I hope someone attaches Bluetooth speakers to their shoes and locks every cart in target, so they have to remove the system.
A market near me included the car park within their geofence, but did not include the (distant) bike racks or the route to them. Sigh... Never before has bringing a full load of groceries home been such an awkward hassle.
The Kroger by my house as these (or ones that look very similar). I generally avoid that store for many reasons, but I’m tempted to go there just to try this out. This is a few years old now; I wonder if they changed the tones.
You can also take a wrench with you, to quickly remove the locking wheel from your cart. Maybe replace it with a non-locking wheel from another cart.
Shouldn't be difficult to find carts left near or beyond the edge of the parking lot.
I find the locking wheels annoying, because they're so often defective and make it a noisy struggle to get your cart through the store. But years ago I also had a neighbor in my apartment complex who would walk home with a cart every week, and would just leave (a dozen of) them there... she couldn't be bothered to push the empty carts back to the store, not even once. I'd think a $1 deposit/return system for carts would work better, and give the homeless in the area some gainful employment.
I suppose now I can admit that we did this in college in 2003 (with RF, not audio), and had great fun seeing a grocery store descend into utter pandemonium, until the power electronics overheated and burned the signal carrier to whose chest the circuit had been taped, who started yelping in the store and drawing a lot of suspicion to himself.
What makes this such a localised phenomenon? Locking shopping cart wheels just aren't a thing here in the Netherlands (or neighbouring countries). It used to be that most required a €1 coin inserted to unlock its link tethering it to the next car in the row, but then covid happened and a lot of shops simply disabled those locks and concluded that the system worked better without — probably driven in part by an increasing number of people who don't carry any cash.
Losing a cart is expensive, but it doesn't seem to happen at the scale that would make a full blown locking wheel solution cost effective.
Not sure if the original site owner will ever see this, but the hit counter they use (counter12 [dot] com) is flagged by Malwarebytes for phishing (and seems to have a history of popping fake virus links? [0])
Is this the same mechanism for signaling lock/unlock as some moving sidewalks use to lock carts in place on the track to prevent you from pushing them?
One of our local hardware store chains, Menards, have ramps in the form of moving sidewalks to allow customers to get fully loaded carts between floors safely and they seem to very reliably lock to the floor at the start of the ramp and unlock at the bottom. I've always been curious about the mechanism.
One unintended consequence of these locking shopping carts is flat-spotted wheels from where they skidded when they locked. Thumpa-thumpa-thumpa through the store, rats, got another bad one.
Hah, this actually works - bookmark payed off! There is one large grocery store near me as well as two higher-end ones. The higher-end ones banned in-store bicycles last year. The large chain store banned them just recently. The area has a lot of car/bicycle thefts and unfortunately the only bike rack near the large one is 30 feet over the property line. Now I no longer have to play a river-crossing puzzle to bag my groceries. As a matter of protest I will be leaving the locked cart near the bicycle rack (but also because an unattended bicycle full of yummy food is begging disaster).
You have to be about 6 inches away for it two work. There are two locks that operate in tandem but sometimes you have to play the tone for both. Also the property line is in the middle of a lane, so a mild safety hazard.
It has occured to me that rather than the complex instructable linked below, it might be easier to purchase an off-the-shelf BTL (high voltage => greater power) amplifier to drive 2W over a small (0.3m dia) air-loop antenna. The AC input signal from the phone's USB DAC is about 0.77V RMS. Let's power the amp with two consumer off-the-shelf 9V batteries in series (18V). Assuming ~1-2 (1.5 here) ohms of internal resistance, the total current draw should not exceed 250mA or the voltage will drop below 8.6V. The loop antenna therefore needs 10 ohms of impedence, and a tuning capacitor to make it resonant (fully resistive). The AC signal needs a coupling capacitor to remove any DC component, followed by a bias resistor to tie the amps signal input to ground. Each amp signal output needs a coupling capacitor because no way will I be able to correctly calculate the tuning capacitance correctly, and also because the antenna won't be a fixed loop. The most efficient use of those 10 ohms is with litz wire, which at 20 awg comes to 300 meters with a 450nF tuning capacitor... which is not happening. Let's shoot for 30m of 20-awg non-litz wire and make up the difference with a 8.8 ohm resistor. 2w across 32 coils @ 10 ohms corresponds to 0.45 A, which at a meter's distance comes to about 0.6 uT... ridiculously tiny. Will it work to activate the circuit? I don't know. However this antenna is simply wasteful - it would be better to switch to a ferrite core design. The magnetic moment of a ferrite core increases more with coil diameter than coil length... but to target 10 ohms resistance at resonance might require a coil length greater than diameter. I haven't really looked into it.
To conserve battery you need an amplifier with a shutoff pin. These are always logic pins (DC on/off), which entails a diode/capacitor/resistor combination tuned to detect and convert AC input to on/off with a configured decay time, i.e. keep the amp powered on for X seconds without signal. Unfortunately the logic pins require high voltage relative to the power source (battery) and 0.77 Vrms just won't cut it. This then entails adding a transistor to shunt power to the shutdown pin from the battery. Then I had a look at a sample schematic of the TPA3116 amplifier, and there are so many pins to wire. At this point the project isn't any simpler than the linked instructable.
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[ 3.2 ms ] story [ 47.8 ms ] threadReminds me of the LoLRa project from cnlohr that transmits LoRa without a radio transceiver.
I hope someone attaches Bluetooth speakers to their shoes and locks every cart in target, so they have to remove the system.
Shouldn't be difficult to find carts left near or beyond the edge of the parking lot.
I find the locking wheels annoying, because they're so often defective and make it a noisy struggle to get your cart through the store. But years ago I also had a neighbor in my apartment complex who would walk home with a cart every week, and would just leave (a dozen of) them there... she couldn't be bothered to push the empty carts back to the store, not even once. I'd think a $1 deposit/return system for carts would work better, and give the homeless in the area some gainful employment.
Losing a cart is expensive, but it doesn't seem to happen at the scale that would make a full blown locking wheel solution cost effective.
I've lived in the US as well and have never seen them there, but it's a big country.
> Since 7.8 kHz is in the audio range
What is "the audio range" in the context of radio frequencies?
[0]: https://www.reddit.com/r/neocities/comments/1i7di1c/help_fak...
One of our local hardware store chains, Menards, have ramps in the form of moving sidewalks to allow customers to get fully loaded carts between floors safely and they seem to very reliably lock to the floor at the start of the ramp and unlock at the bottom. I've always been curious about the mechanism.
You have to be about 6 inches away for it two work. There are two locks that operate in tandem but sometimes you have to play the tone for both. Also the property line is in the middle of a lane, so a mild safety hazard.
To conserve battery you need an amplifier with a shutoff pin. These are always logic pins (DC on/off), which entails a diode/capacitor/resistor combination tuned to detect and convert AC input to on/off with a configured decay time, i.e. keep the amp powered on for X seconds without signal. Unfortunately the logic pins require high voltage relative to the power source (battery) and 0.77 Vrms just won't cut it. This then entails adding a transistor to shunt power to the shutdown pin from the battery. Then I had a look at a sample schematic of the TPA3116 amplifier, and there are so many pins to wire. At this point the project isn't any simpler than the linked instructable.
Then I found this:
https://www.rockvilleaudio.com/headrock/
According to the website it requires a minimum load of 16ohms, but that might be ideal for ferrite-core antennas. Perhaps I'll give it a try!