We open the doors of our Electronics Workshop to teach you to mount a digital voltmeter . A simple electronic assembly used to measure any DC voltage from 0 to 100V . You just need some components very easy to find and want to put you to work.
All electronics hobbyists must be between its tools some basic equipment. A power supply and a multimeter are essential. The power supply can be mounted manually, be advisable to incorporate a simple voltmeter indicating the output voltage us.
This time we teach to ride a small digital voltmeter to measure any current between 0 and 100V. This circuit can be used in any assembly and modified to suit other needs. In any case, this time the voltmeter is suitable for measuring the output voltage of a power supply.
How does it work?
In the electronic fitting scheme it can be seen that the circuit is powered by 5v regulated . They can be applied by means of a regulator (uA705) of the same power supply.
The voltage to be measured is applied to pin 11 of U1, by a resistive voltage divider formed by resistors R2 and R3. This reduces any divisor input voltage by a factor of 100. As the chip U1, is the analog-digital converter designed to convert the measured voltage into a digital value BCD.
The capacitor C1 is part of the chip internal integrator. The Potentiometers P1 and P2 form settings maximum and zero respectively.
The U2 is a BCD decoder chip seven segments with integrated limiting resistors, which is responsible for turning on the segments of the displays according to BCD code supplied by U1. Employees displays are common anode type.
The segments of the displays are connected in parallel, as each digit is selected and activated in successive order through the circuit. In this case the scan rate of the display is 386 Hz.
Assembly instructions step by step
For mounting plate can be used islets. The main board has no problem, rather than the assembly of all components and the 5 bridges thread. To connect the display must be adapted to particular model used.
To facilitate assembly, we fitted the displays on three small sockets 7 pin to which we removed the remaining pins with cutting pliers. For the connection between the two plates is recommended to use flat cable of the type used in computers. This cable is soldered directly to the segments of the central display. Once assembled and conexionadas the two plates, it is necessary to check and adjust the circuit. To feed the voltmeter, a voltage of 5V (not worth another), we can obtain from a controller uA7805 type is required. * This type of regulator has been published in previous productions of this section.
As voltage to be measured, we can use any stack of a known value, for example a 1.5V or 4.5V. We remind that this circuit only measures currents (never alternate) and positive value with respect to ground ; ie not worth negative voltages, so you have to respect the polarity at the entrance. The input voltage divider must be adapted to the voltage to be measured, for high values must multiply the value of these resistors with a value of 10 or increase the power thereof to 2w. Therefore, before applying power to the circuit must conform to P1 and P2 halfway.
For proper operation of the circuit is required two adjustments. For the first adjustment, must short the input to ground, and adjust P2 until the display reads 00.0. Below be applied to the input voltage of known value (for example 4.5V) and adjust P1 to read on the display 04.5.
At this time the circuit is set and ready to go. In our assembly and voltage measurements low value (less than 50V), the divider formed by R3 and R2 comprises two resistors 82 and 8K2 ohm ½ w. To measure higher voltages (up to 100V), these resistors must be replaced by other value 10 times (82K ohms and 820). Or increase the power of them, otherwise these components would be heated and could get burned.
You Do not stop learning electronics!
In Todoelectronica magazines you can find this and other electronic assemblies detailed step by step. So while this is an entertaining and practical to learn electronics and automation apply different shape our projects.
Also with the electronics course you can learn everything you need to start your own electronic devices go. Of course, if you have any doubt, consultadnos without obligation !