In the circuit, use only metal film resistors (MFR) of 1 per cent tolerance, as this is an instrumentation application. Power supply should be a stable +5V, -5V supply, for which one can use 7805 and 7905 regulators.
Thermocouple Temperature using DPM or DMM
The inputs TC+ and TC- terminals should go to a 4-way barrier terminal block, the 2 extra terminals are used to mount TH1 Cu thermistor. This forms an isothermal block, which is good enough.
This is a Test Circuit for Logic Analyzer software, with the Simple port circuit. The VB Logic Analyzer works, but is just an example program to test and learn.
Test Circuit for Logic Analyzer software - del20006
The speed at which the logic state changes say like 10 M Hz while probing even a PIC or 89C51, is too fast for this circuit. For that, the incoming data has to be spooled or stored in RAM at real time, by the external Hardware itself.
Volume control circuit for speaker 4 ohm or 8 ohm located in the another room far away. by using only passive components. This gives limited control and helps reduce volume when a conversation starts. The resistors are very low value.
Passive volume control
A simple circuit you can build at home at low cost it uses just a rotary switch and wire wound resistors. Add more resistors and a rotary switch with more contacts for finer control.
More Hobby Ideas and Projects at Hobby DIY Garage
U3 LF 356 is used as a constant current source (sink as the current is negative). R4, R5, R7 and R9 set the four resistance ranges by changing the constant current in decade steps. R2 is for calibration of resistance range. The A-B digital control of 4052 selects the range.
Resistance measurement - DMM Project
Let voltage current and resistance sockets be separate and of different color or use a high voltage electrical rotary switch or relays if you want the same sockets switched. D1, D2 and R8 are to ensure that the FET can be turned off, as the opamp swings from +/- 3.5V only, with some FET it needs to be tweaked.
Here the 4053 selects or routes the voltage, current or resistance measurements to the A-D converter or display. It is selected with the mode selection when you want to measure Volts, Amps, Ohms and AC-DC. Some have to be polarity inverted and some signals just buffered this is selected and done by this circuit according to the digital control.
Analog Buffer and Inverter Switching
Now U1 OP07 circuit is a Buffer unity gain and low offset, U2 circuit is unity gain but polarity of output is opposite of input. D1-D2-R3 form a AND gate to select diode-buzzer test mode. The digital selection of 4053 Analog-Switch does not produce any errors in the analog-switching of even mV signals. But it works best at +/- 7.5V dual supply pin-16 is +7.5V, pin- 8 is digital ground and pin 7 alone should go to -7.5.