Digital current table for automatic replacement range, Digital AMMETER
Keywords: digital current table with automatic replacement range
Digital current table that can be automatically replaced
Do this circuit is to improve the voltage regulator power of my own home. Now the voltage regulator is improved before the improvement, it is quite ancient, and this power is older than me. It is going to be, but it is going to be When the inside is opened, the inside of the inside is genuine, very good for dozens of dozens ago, so I still improve it, use it, this article is mainly recorded for this power supply current meter..
Look at the finished product, because the 0.02Ω resistance is hard, with a lot of 0.1Ω resistors to get in parallel, there is a little ugly.
Front view:
Bottom view:
The first is a current detection part of the circuit:
The detection resistance used in current detection is only 20 millio. It is difficult to find. Therefore, I chose 5 0.1Ω resistors in parallel when making it, because I didn't give these electric resistors when I designated it. Space, I used to use a copper wire to do current sensors, but the electrical resistance of the copper wire is determined, the fine copper wire is easy to heat with the measurement, the thick copper wire is large, can't put, finally use 0.1Ω resistance Parallel, anyway, after installing it into the power supply, can't see the appearance outside.
20 m-mill resistance sampled voltage is enlarged by precision op amp, which is 28, and automatic switching range can be achieved when the current is 1.8A, because it is used, the requirements are not so high, 2A Switching the range or 1.8A switching range does not matter, then just make a large multiples 28, of course, if you want to switch the range, you need to make a larger bit, you can reduce the R3 resistance.
The R4 in the circuit is used to zero. When there is no current, adjusting the 6 foot of the OP07 to 0V when no current, of course, this adjustment needs to use the digital multimeter, the pointer is not accurate, and the voltage to be adjusted in this article must use the digital multimeter Row.
In the printed circuit board, R4 is divided into three resistors, respectively, 5K adjustable resistors and two 7.5k patch resistors.
R12 is a small current range (less than 2a) fine-tuning resistance, a given operating current 1.8a, then adjust the resistor, the header indicates that the header is OK, and may of course be, but it will not be large. Similarly, R9 is used to adjust large current range.
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LED display partial circuit:
This circuit uses two red two-position common anode digital tube
ICL7107 Voltage Measurement Some Circuit:
The voltage measurement part of the chip uses ICL7107, it is very cheap, Taobao is a lot of money, and you can buy it.
Please select the part according to the parameters in the figure, pay attention to the ceramic capacitance, use polyethylene polypropylene capacitance, the worst allows the use of polyester capacitance, otherwise affect the measurement result, I will follow the minimum requirements, take the polyester capacitor, huh,
The resistance is not required, as long as it is enough, it is at least 1% accuracy.
When the circuit needs to adjust the resistance of the R20, it is possible to make 36 foot voltages of 100 millivolts.
Test Head: Be the simplest power supply, output 150 millivolts, 100 millivolts, 50 millivolts, input to "in" in the circuit, see if the display is correct, if a bit error can be fine-tuned to see the following R20 Is there a result.
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The head is called, you can debug the whole machine. First, adjust the R4 to output the OP07 to 0V, then output 1.8A current, then adjust the R12 to indicate the header to 1.8A, then output 5A, adjust R9 The head indicates that 5A, simply debugging, it should be used in the experiment.
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Part installation:
Note that there are several jumpers in the figure.
Some resistance capacitors are required in the underlying layer, and the resistance capacitance is encapsulated in 0603. The chip is also welded in the bottom, this should be paying attention.
The entire circuit is powered by ± power supply, and it is enough to use ± 5V.
Forgot, the model used by the relay is: HK19F-DC05-SHG or HRS2H-S-DC5V, of course, you can also choose another 5V power-type relay, but if you follow my PCB file to do the board, you may not install it. Go up.
Attachment has a PCB print picture, a positive map and a negative map, choose it yourself, I use a negative map, do it with the photosensitive plate, if it is hot transfer, please use a positive picture. The negative map is trimming, so the copper trace will look better than the positive pattern.
The PCB print picture is a PDF format file.
Again, there is a flying line between the r16 and relays on the board, this flying line is used to use the shield line. Don't forget to connect, if this doesn't measure it. If you have any questions, you can leave a message in the QQ group.
Download PCB files in PDF format: Current table pcb.pdf
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