Strange behaviour of local car wash timer  - Page 1
Forum section: electronics / general

author: xrunner
author_rank: Super Contributor
timestamp: August 01, 2024, 09:51:45 pm
content: Went to the local car wash today - same one I've used for years. I set my quarters down and was ready to put them in when I noticed the wand already had some water coming out. I pressed the wand trigger and it sprayed at full power as you would expect. I quickly glanced at the timer display (red LEDs) and it looked like it was at 2:00 minutes so I set the dial to "soap" and proceeded to wash the car. Guess someone put in a bit too much money - oh well my lucky day right?I washed with soap and then went to switch the dial to "rinse" and I was amazed when I saw the timer indicating 22:00 minutes. WTF?Oh - I now think it was showing 20:00 when I first glanced at it and I must have just brain-shifted it to 2:00 minutes because that was what I was expecting. But here's the weird thing - after I realized how much time was on the display (it was a larger number than when I first looked at it) I stared at it and it was counting up not down! I wonder how long that was going on. May have started earlier in the day with the first deposit of money and due to a logic failure it just kept counting up.I asked a guy that was cleaning out his car interior if he was going to wash it, and I told him to get in line behind me if he wanted a free wash. I wish I could have gotten inside that control box to see exactly what was going on to make it count up and not down. Never seen that one before.

author: Psi
author_rank: Super Contributor
timestamp: August 01, 2024, 10:34:30 pm
content: This is why you should always use if (i <= 0) and not if (i == 0) when checking if something (like a timer) has reached 0.Otherwise, if it ever becomes negative via some bug it will keep getting more and more negative as you keep subtracting 1 every second.Even if your code has no bugs a cosmic ray hit could make it negative (assuming its a signed variable of course).

author: Halcyon
author_rank: Unknown
timestamp: August 01, 2024, 11:56:57 pm
content: It'd be interesting to know what the trigger was. Perhaps there's some kind of upper limit to the time (to prevent hogging the bay), which caused the counter to go to some unexpected value? Or maybe someone sprayed water in there?

author: xrunner
author_rank: Super Contributor
timestamp: August 02, 2024, 12:15:31 am
content: Quote from: Halcyon on August 01, 2024, 11:56:57 pmI never thought about how high the timer could get if you deposited a whole lot of coin. Who does? I don't think I've ever put in more than $2 of quarters. I don't really know how long I want to use it when I pull in so I don't buy all the time I need at the beginning. The minimum to get it started is $1.25 and I think it buys you 2 minutes. But at any time you can deposit more quarters and get the time added on to what's left on the display. I'd be neat to find some weird hack about the way it responds to the money being added on. Maybe somebody happened onto a bug in the way it adds time.But there must be an upper limit if you ever wanted to try but who would waste the money. If I remember I'll go back and see if I can find out the manufacturer of the car wash system. I should have taken a pic of the display just for a memento.

author: Halcyon
author_rank: Unknown
timestamp: August 02, 2024, 01:00:40 am
content: Why don't you speak with the manager, explain the situation, tell him you're an EE and offer to debug it for them. I wonder how many of those systems were installed 20+ years ago, and apart from some basic maintenance, haven't really been updated. You'll probably find an old EEPROM in there.

author: floobydust
author_rank: Super Contributor
timestamp: August 02, 2024, 01:32:38 am
content: Quit being honest, exploit the bug lol.Manual car washes here have tap-n-pay for credit/debit card, it's $2 per couple minutes or so session.You can increment (+/-) the number of $2 sessions to charge to your card when you tap. i.e. up it to say $6 for a 6 minute session.I'll bet the F/W bug is when you decrement below 1 session or something, or the clear of that variable when time expires.Once I found the wand was already enabled, so I kept washing the car for free. I didn't pay attention to the time display though.Finished it was at least $8 for the wash, foaming brush, rinse and it was still going.edit: I can't find the tap-n-pay terminal manufacturer, it's custom because of the waterproof buttons and enclosure.

author: RJSV
author_rank: Super Contributor
timestamp: August 02, 2024, 06:36:54 am
content: OMG ! I'm just speculating (the worst) but what if someone earlier had used a credit or debit card, and it somehow remained actively deducting a cash balance, while adding to the timer run value...?A bit unlikely, but I suppose more weird situations like this have happened!A person from couple hours before, would then be in a situation where the bug caused a '$55 dollar debit....

author: xrunner
author_rank: Super Contributor
timestamp: August 02, 2024, 10:48:29 am
content: Credit cards? This car wash don't know nothin' about credit cards.The control box knows quarters and that's it. You ain't got no quarters today? Well you can go to the center control house and out front they got a change machine that'll give you quarters for dollar bills. You ain't got no dollar bills? Go home. No, this is basic technology, and the control boxes are pretty beat-up. They have old style chicken head knob that selects your desired cleaning fluid or rinse water (plain water or spot-free rinse).You know, I tried (or attempted to try) one of the newer car washes where you can drive through but I don't like their payment policy. I drove up and asked to get a car wash one time to try it. I was going to pay in cash for one wash. The guy said - well we accept credit cards only, but it's a payment plan per-month. You can wash your car as many times as you want to for $xx (I don't remember the price) and we'll charge your card automatically each month until you cancel. I said I don't want that I just want to wash my damn car one time every so often and pay for the wash. Oh we can't do that kind of payment sir. No, we don't want your stinkin' money that way.

author: tom66
author_rank: Super Contributor
timestamp: August 02, 2024, 11:01:04 am
content: Hypothetical but sometimes systems like these are based on off-the-shelf individual units, so the manufacturer of the car wash equipment just buys in an off-the-shelf timer and display module, which takes a trigger input from the payment unit and turns on a relay to enable the washer functions. The timer might have some configuration that caused it to count up instead of down (I can imagine there would be some applications that require an up-counter-and-alarm kind of function), perhaps it was misconfigured by the last maintenance tech or water got into the casing and the DIP switch which controls the settings has gone all funky.

author: Psi
author_rank: Super Contributor
timestamp: August 02, 2024, 11:32:43 am
content: Quote from: tom66 on August 02, 2024, 11:01:04 amSome water ingress and corrosion shorting the timer pin that controls count direction seems quite plausible.

author: xrunner
author_rank: Super Contributor
timestamp: August 02, 2024, 01:31:14 pm
content: Indeed - lack of maintenance would be my first choice of the cause. The boxes are in pretty bad shape. The one which I used was beat up and the knob didn't turn very well. I'll try to go by there this weekend and take a pic of the box, maybe we can find out who made it.Hey and if the thing is still malfunctioning I'll get another car wash!

author: themadhippy
author_rank: Super Contributor
timestamp: August 02, 2024, 02:37:52 pm
content: QuoteIf its unstaffed i'd get a hi viz vest with attendant on the back and be down there charging $2 a wash

author: SeanB
author_rank: Super Contributor
timestamp: August 02, 2024, 04:25:18 pm
content: You have to wash your own car? Car wash by me is $2 Mon to Wed 9AM to 3PM for a full wash, and interior clean, all done by hand. Outside that it is $3, and for a SUV or pickup it is $5 at all times. Pay by cash, or using the ubiquitous mobile terminal using your card to tap for it. They do prefer cash though......

author: RJSV
author_rank: Super Contributor
timestamp: August 02, 2024, 05:27:52 pm
content: thermhippy:(You mention High Visibility Vests):Here in beautiful, homeless capitol of U.S.A., I noticed that those high vis vests have been a popular item, for 'unhoused' residents, combing the streetscape. An unexpected fashion avenue these days,...'Homeless Chic'.

author: floobydust
author_rank: Super Contributor
timestamp: August 02, 2024, 09:09:30 pm
content: Some OHS safety requirement around the age of safety clothing - it's supposed to get thrown out after a few years and I think street people, homeless gather them.One employer changed the flammability (fabric thickness) requirement and it was all new vests, coveralls etc. Huge expense.I think I pay $1/minute for the pressure wand, vac cleaner, foaming brush etc. There is no pause button. Coins are long gone, they had changed to tokens which were a stupid hassle but it stopped crime, people busting into the coin boxes.Next time I will mess with the credit card terminal and see if I can get it to the land of the free.It maybe just a non-atomic condition, the timer is running and decrementing- when a valid card tap occurs and is supposed to increment it.Or the (tap) amount to increment is corruptible, I'll see if I can get it to zero lol.It seems to wrap around.

author: thm_w
author_rank: Super Contributor
timestamp: August 02, 2024, 09:37:23 pm
content: Quote from: tom66 on August 02, 2024, 11:01:04 amYeah makes sense, old school coin units would just send out a pulse when you insert a coin.https://www.adafruit.com/product/787Presumably the coin unit itself is working OK.