How to Power a Multimeter with a Linear Transformer
The 9V battery of the multimeter is very fast and not cheap. Many people use lithium batteries to power multimeters. Although there is no need to change batteries all day, the lithium batteries may be ruined if they are not careful. I have two multimeters, one is fixed on the table, so I can power this multimeter with a linear transformer, which saves time and effort, as long as there is mains power, the multimeter can be used. If not, the battery can still be used. Well, after introducing so much, let's start talking with practice.
▲First of all, the circuit diagram is shown first. As long as the linear transformer is larger than 9V, it is enough to multiply the voltage by 1.414 times after rectifying and filtering, which is enough for the voltage regulator chip.
The voltage regulator chip can choose 7809, preferably this kind of linear voltage regulator, the ripple is small, it has no effect on the multimeter, and the switch is not easy to say. can choose
Smaller than 7809, the reason is on the picture
▲The materials are all in the picture above. The capacitor should be about 2 times the voltage after rectification by the transformer, and there should be a margin.
▲Prepare to solder the power cord to the transformer
▲After welding, wrap it with heat shrinkable tube insulation or electrical tape
▲The measured output AC is more than 14V
▲Go to the hole board project below, first weld the rectifier bridge
▲The picture shows a 1000 microfarad capacitor, but I suddenly found that my capacitor is not enough withstand voltage, so I replaced it with 5 100 microfarad capacitors, the effect is similar
▲Not welded neatly
▲After soldering on the voltage regulator chip, my voltage is not enough, so I need to add a resistor
▲Come on, the voltage regulator chip shows its face
▲ Cut the long pins
▲Basically good
▲Solder the input and output lines
▲If you don't care about appearance, this is fine, but I want to make him a home
▲ first measure the voltage, qualified
▲ Ready to put into the box
▲Cover, this is a ballast box
▲Attach a label
▲Connected, can work
▲(Left: Transformer power supply Right: Used for parameter measurement) Connected to the multimeter, the voltage did not drop much
▲Turn on the backlight, the voltage is 9.1V
▲The buzzer consumes more power, but it still does not drop 9V
▲Beep plus backlight, down to 9V, but it has no effect
Well, after reading what I have done, are you a little excited, so let's make one!
