Calibrating a Cheap Digital Thermometer

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et's say you're relaxing some evening, enjoying a few homebrews, and shopping eBay. With some beer logic, you click BuyNow on a digital thermometer for $1.83 (free shipping!) from a seller named Hola-Fly in China. Let's say, you forgot you ordered it and eight weeks later it surprises you in the mail ...but to no surprise it's not very accurate.

Okay, let's say I did this.

My plan was to install it in my beer fridge so I could keep an eye on my beer temp. If Coors Light drinkers can have their "certified cold" mountains, I should at least have a thermometer. Unfortunately this cheap little thermometer measured about 4°C too warm. And of course, since it costs less than a large coffee, there is no setting to calibrate it.

The probe is likely a simple thermocouple but could be a resistance thermometer - either way it's effectively a variable resistor affected by temperature. I figured I might be able to increase the resistance to get the results I needed.

I cut the lead and spliced in a 5KΩ trimpot (trimmer potentiometer) to one of the wires and dropped it in the fridge along with another thermometer that I trust. Waiting 10-15 seconds after each adjustment, I tweaked the trimpot until I was consistently getting the correct reading. With the trimpot removed, I measured it to be set to 2.2KΩ. I didn't have a 2.2KΩ resistor ( ▌▌▌) so I used a 1.2KΩ ( ▌▌▌) and 1KΩ ( ▌▌▌) in series. A little soldering and heat shrink and it's all good.

I should point out, this isn't really "calibrating". I just increased the resistance across the entire range - I'm betting it's not a linear relationship between the temperature and the resistance. However, it's now pretty accurate in the 0°C - 10°C range (above 10°C it starts to deviate). Good enough for a beer fridge.

1959 VW Ad - Gerhard Baecker teaches Volkswagen

©1959 VOLKSWAGEN  *SUGGESTED RETAIL PRICE
Gerhard Baecker teaches Volkswagen
(Or why Volkswagen service is as good as the car)
Gerhard Baecker, schooled in Wolfsburg, Germany, now teaches Volkswagen in the United States. Like most teachers, Gerhard be-lieves in what he teaches. He shares whole-heartedly the Volkswagen philosophy: the car is only as good as the service it gets. As a result, you'll find Volkswagens are serv-	iced only by graduate mechanics trained to demanding Volkswagen standards. Volkswagen service is fast. Your Volkswagen engine can be removed and replaced in 90 minutes. A fuel pump installed in 20. Every authorized Volkswagen dealer has a complete inventory of VW parts on hand.	There's no wait, no substitution. Volkswagen parts are inexpensive. A new front fender is $21.75,* a cylinder head $19.95.* If you've been thinking about buying the Volkswagen, isn't it nice to know the service is as good as the car?

1962 VW Ad - The Volkswagen Theory of Evolution.

©1962 VOLKSWAGEN OF AMERICA, INC.
The Volkswagen Theory of Evolution.
Can you spot the Volkswagen with the fins? Or the one that's bigger? Or smaller? Or the one with the fancy chrome work? You can't? The reason you can't see any revolu-tionary design changes on our cars is simple: there aren't any. Now, can you spot the Volkswagen with	the synchromesh first gear? Or the one with the more efficient heater? How about the one with the anti-sway bar? Or the more powerful engine? You can't? The reason you can't see most of our evolutionary changes is because we've made them deep down inside the car.	And that's our theory: never change the VW for the sake of change, only to make it better. That's what keeps our car ahead of its time. And never out of style. Even if you aren't driving the most evolved VW of all. Our '63.

1961 VW Ad - No point showing the '62 Volkswagen. It still looks the same.

*SUGGESTED RETAIL PRICE, EAST COAST P.O.E. ©1961 VOLKSWAGEN OF AMERICA, INC.
No point showing the '62 Volkswagen. It still looks the same.
No heads will turn when you drive a '62 Volkswagen home. (Maybe an eagle-eyed neighbor will notice that we've made the tail lights a little bigger. But that's the only clue.) Everything is right where we left it in '61. Including the price: $1,595.* Inside is another story. We've put all our time and effort into	improvements that matter. The '62 VW runs more quietly. There are new clutch and brake cables (as well as new steering parts) that never need maintenance. Heater outlets front and rear for more even heating. Easier braking. And 24 more. One change is literally a gasser. We've added a gas gauge. Our first.	A few die-hards may think we've stolen some of the VW's sporting flavor. But the gas gauge may be more useful than you'd imagine. It will not only tell you whether your tank is E or F; it will prove you're driving a '62. It could make 1962 go down in VW history as the year of the big change.

1956 VW Ad - Why the engine in the back?

Why the engine in the back?
In conventional cars, a front engine turns the rear wheels through a long drive shaft. But Volkswagen's rear engine gives direct power to the wheels, saving weight and power. It is the most efficient and eco-nomical design. It means greater visibility when driving - you see over VW's snub nose. And the rear engine gives your rear wheels better traction.  In mud, sand, ice,	snow, where other cars skid, you go. Its location, however, is the least un-usual feature of a Volkswagen engine. For one thing, it is air-cooled, an astonish-ing advantage when you think about it. No water to boil over in the summer, or to freeze in winter. No anti-freeze needed. No radi-ator problems. The engine is ingeniously cast of alu-minum and magnesium alloys and is very	light and powerful; undoubtedly the toughest 198 lbs. going. It is beautifully machined for minimum friction; you will probably never need oil between changes. And so efficient that top and cruising speeds are the same. Your VW runs at 70 mph all day without strain. You get an honest 32 miles to the gallon (regular gas-regular driving).