Resistance Measurement Analog LED Meter

This is a LED Analog Meter, This can be used as a Resistance Meter and Low Impedance Voltmeter for Battery Levels. To measure battery voltage, the R5-R12-R17 etc. part of the Reference Resistor Divider Network can be modified to suit. Shown here is for 4 LEDs, Use Three LM324 for 12 or More LEDs and Cascade as shown.

Resistance Measurement Analog LED Meter

This cannot Measure Voltage levels from High Impedance Sources, will work for Battery Voltage Tests. To make it into a Continuity tester. R27 must be a short and R23 5 Ohms. The Black probe should have a Built in Resistance of 2 Ohms. If you want it to be a dedicated voltmeter, remove R3, The Probe has to be a 10X Attenuator with 10M Ohm and The Resistor Divider Steps in 100mV per Step. The R27, R23 etc. is 20K. A Leakage Tester a Mains Voltage Monitor are other possibilities. Use LM3914 for a easier solution. A nice book for your Design Library – Measuring Circuits By Rudolf F. Graf

Analog Level by BCD Thumbwheel Switch

BCD Thumbwheel Switch is used to input-set data in digital form, this can be read by digital circuits, uC and uP systems and PLC-SCADA Interfaces.

In the early transition of analog to digital, before uP became acceptable, Digital systems without uP were made, it even had printers, RAM and displays. The uP systems were coming in, uC had not yet come and uP systems had to still win the confidence of the Prudent Industrial Design Engineer.

The drawbacks of uP based systems used in Computers, in those days were.

  • Power Consumption was very high, needed SMPS.
  • Many chips, a CPU had a Retinue of many chips.
  • Large Board, Double or Multi Sided due to Bus.
  • Fussy, Hangs on minor Power Glitches or Resets.
  • Needs Firmware Development and Tight Testing.
  • Investment in all these areas, Tools and Manpower.

These made Industrial Automation with uP a challenge. CMOS digital and mixed devices and custom application devices were more easy to implement and affordable.

The coming of Low power CMOS uC changed everything and embedded systems became smaller and robust. These were packable in DIN standard and DIN Rail Mounting enclosures.

Coming back to inputting digital data. CMOS uC and Ni-Cd Battery backed up RAM with keyboards made thumb-wheels and other methods less attractive for digital data inputs. Then the Li-Ion Battery, Flash Memory in Combination with Application Specific uC and SOC have made inputting, retaining digital data very easy and affordable.

Thumbwheels are mechanical memory like DIP switches, but have limited number of operations. Flash is Mechanical Noise immune, vibration will not shake the bits out of it. Thumbwheels are Electrical Noise Immune, data will not be corrupted due to Spikes, Glitches, EMI, RFI and Power Supply Failures. Yet thumbwheels cannot input or store an entire page of data.

Here is a Circuit that will help you understand or learn practically Digital to Analog Conversion. Practical Learning is very important for Technical Education. So you can easily wire this up and learn. This is an Inverting Op-Amp where Ri is varied using TWS. Vref can be from LM336 (-2.5V).

Analog Level by BCD Thumbwheel Switch

Ignore the DIP Switch part, When a 10 Turn Bourns Pot is used in place of Thumbwheel for Setting the Value, the DIP switch settings are changed.

(Information above is presented for edutainment purpose only, to create an appetite for learning – Cross Verify your learning acquired, from other Sources – delabs)

Millivolt Source – Field Calibration Current Loop

This is easy to rig millivolt source for field calibration or troubleshooting of 4-20 mA current loops. Here a Darlington pair is used for current amplification which reduces the Ib error as gain is very high.

Millivolt Source - Field Callibration Current Loop

A rotary switch selects, 4-12-20 mA Preset points. A Bourns multi-turn wirewound Pot can also be used with a digital dial. Enclose in a dust proof handheld box. Read more on process calibration.

Opamp Supply on Buffered Virtual Ground

When a Inverting Opamp Configuration is at a steady state, we say the Inverting Input is at a Virtual Ground. That means it is at 0V w.r.t to the dual power supply ground, but it cannot drive or draw any current. It is at a high impedance, but still at 0V. When you buffer this 0 V, you get a low signal ground for a opamp supply.

Opamp Supply on Buffered Virtual Ground

This gnd. can sink and source in a couple of mA. You can use it with low power opamp circuits for portable battery operated devices. This creates a virtual +/- 6 V dual supply from a 12V battery. This may be needed in cases where some instrumentation opamps need the negative supply or your design demands a measurement around zero. You may get a more loadable ground using a Power Opamp, i have not tried. The above circuit gnd cannot be used as a return path for LED’s or Relays. You can drive these, between VCC-VDD, but translate levels to drive them.