Tuesday, May 09, 2017
See the Circuit Full Size - Microohm Meter with LED Analog Bar
This has a 9V battery power. The 555 spins and a negative voltage for Opamp is created. This is a Low Offset amp of OP37 of Precision Monolithics, Inc PMI an early innovator. This diff-amp amplifies the uV of a 4 wire resistance measurement.
Now the current pump is the 2N2222 you see above the OP37. The FET and 555 do synchronous rectification. The LM324 is the Indicator and Analog to LED Dot-Bar Converter. The probes are Gold Plated, or use solid gold pins if you have them in plenty.
Monday, June 13, 2016
Bill O'Donnell - Tech Gizmo Builder
These projects are advanced and not for a beginner student or newbie hobbyists. These pages are knowledgable and will help students and DIY enthusiasts understand more about Lasers, Precision Temperature Control and stepper motors among other things.
Auto Fill Circuit for Laser Cooling Loop - Ethernet Data Logging
Here is an automation solution with a ethernet usage. The code and diagrams are also there. This is something that covers many aspects of engineering in one project. Try such things out to learn, only after you have mastered the basics.
"The Ethernet connection is based on an XPORT form Lantronics. Basically it lets you use a serial port to send things over Ethernet. A PIC microcontroller with an A/D converter digitizes the pressure, the pressure set point, the high and low pressure alarm points and the supply voltage (since everything is ratio-metric). "
Saturday, September 05, 2015
Measuring the temperature of a body, depends upon the establishment of thermo-dynamic equilibrium between the body and the device used to sense the temperature. In practice, this condition is rarely attained since it is difficult to establish complete instantaneous equilibrium. Hence great care must be exercised in choosing a method suited to the problem so that satisfactory conditions for temperature measurements are obtained. Temperature sensors possess thermal characteristics dependent largely on their size and shape and the materials from which they are made.
These characteristics affect precise measurements. The introduction of a temperature sensor into a body tends to modify the temperature conditions at that point. In most cases the sensor is connected to a recording instrument by means of an intermediate system, along which the signal is carried. The intermediate system and the recorder may be subject to temperature and other changes. Hence compensating devices become a necessity to reduce or eliminate errors.
The measurement of temperature in our instrument depends on the fact that the forward voltage drop of a silicon diode changes by about - 2 millivolts per degree centigrade. Thus, by measuring the change in forward voltage of silicon diode kept in a temperature probe, the voltage drop can be converted into temperature.
Since this involves the measurement of millivolt level accurately a precision voltage source is needed. This can be conveniently obtained from the 3 pin + 5v voltage regulator. This voltage is tapped using a preset VR6 whose output is used for adjusting the ice bath temperature reading to zero degree. This tapped voltage is fed to the diode in the temperature probe and the other end of the diode is returned to a negative supply of -8v. The negative supply uses a (-8v regulated output from IC 7808 voltage regulator) which has the least variation with temperature. Now, the voltage at the probe point is connected to the input of DPM via function selector switch ST.
The temperature probe can be made by a length of shielded audio cable connected to any type of mini plug and fitted onto the front panel socket SSG/T. The free end of the cable is soldered to the diode. The diode is kept just at the tip of the cable. A miniature glass diode like 1N4148 is preferred. The soldering makes a good fixture at the end of the cable. The meter can thus measure temperatures from 0°C to 150°C continuously and upto 200°C momentarily since above that the cable starts melting.
Epoxy Resin and a used Metal Pen Refill can be used to make a sensor to insulate the cable. The diode must be thermally and electrically isulated from metal tube.
(above text may have ocr and concept errors)
Extra Reading -
Saturday, April 26, 2014
Open Source Android Oscilloscope
Using USB, the hardware plugs into Android devices that support USB Host. Together with the OsciPrime Android oscilloscope application it turns a tablet or mobile phone into a high speed data acquisition system.
- 2x Analogue Input @ 8bit/6Msps
- 5 analogue gain levels
- 3.3 MHz - 8.0 MHz Bandwidth (gain dependant)
- 16 V Max Input Voltage
- 880 mW Power Consumption
- Designed for 10x Probes
Controls -V-Offset, Time-Offset, Calibration; Trigger Controls Falling/Rising and Edge, You can Measure Voltage, Freq and Period.
- Range +/- 1.5 V up to +/- 16 V
- 5 us/Div max - 1 ms/Div min
- Processing 400'000 samples per second
Tuesday, May 17, 2011
I wanted to design a logic probe as a tutorial, but there were many good ones in the web so i have tried to design a single digit voltmeter. This circuit is a design, i am unable to test it now, later if i test it and find mistakes i will update this page. You can help me by pointing out the errors.
Single Digit Voltmeter with LM311
First bear it in mind that it is a single digit voltmeter which is 0-9 counts only on the positive side, that is it can measure +0 to +9V DC +/- 1V error. That may not be practical for the cost of the components above. It may be used as a toy logic probe. The reason for the circuit is not for usage, but to give design ideas. The methodology used is Gut Feel - Thumb Rule method.
First i explain the simple part, D1 a seven segment common cathode LED display is chosen as CD4511 is a sourcing driver. 4511 can be latched so it has been used here, it decodes binary 4 bit decade info to seven segment output. The four bits are derived from CD4029 up-down clock pulse counter. LM311 is a analog comparator with single supply capability which is the A-D interface.
To avoid resistors for each of the LEDs the LEDs are turned ON-OFF at 10KHz 50% duty cycle. The Nand Schmitt Trigger CD4093 is used as in IC4D as a 10KHz Clock which drives T1 transistor with a resistor R5. On turn on IC4D one input is high which is pin 12 pulled up to +5 and another Pin 13 is Low as C4 is in discharged condition in NAND gate both inputs high, gives a low output, the other combinations the output is high. So the output goes high, this starts charging the cap C4 which soon makes both inputs high, which in turn makes output low starting the discharge of C4. This is now evidently a endless loop, hence it is a oscillator. R*C = T .... 0.01uF * 10K = 100uS or 10KHz as F=1/T approx or better still multiply by 1.1 ?. I am not good at formulae but i manage with a calculator.
The supply and ground pins of CMOS chips have not been shown, see datasheet or earlier circuits.
IC4A is also a oscillator but slower which is good enough, it is slow so that a measurement can be made nearly every second. The IC4A slow clock is read by 4029 which produces a count-down binary nibble at Q1....Q4, This is converted to crude analog with R1...R4. The voltage generated is compared with the voltage you are measuring by LM311 which generates a Latch pulse to 4511 to freeze the reading where both voltages match.
Method of Operation :
IC2 is a Counter in Decade-Down mode and IC3 is a BCD to Seven Segment Decoder which Drives the Display D1. The Circuit is wired in such a way as to keep counting the Pulses from the Clock IC4A. The IC4A which is wired as Schmitt Nand Oscillator Clocks the Counter. Now to understand how this Counter and display works see this Interactive Tutorial Simple Digital Counter. For every pulse at Pin-15 of 4029 the Counter Counts down from 9-8-7-6.... and so on. But the Display is Latched by IC4C, So the Display is static even when counter is running. So while testing counter you can remove IC4C and keep LE Pin-5 of 4511 low to ground. For testing this Circuit you can use the manual clock with a pushbutton (single step) or a slow clock rate 1 Hz as in the Tutorial Simple Digital Counter.
The Transistor T1 and Oscillator IC4D is to chop the power to display at a fast rate, this avoids the adding of seven resistors. This is not required, but it saves power and reduces parts count. IC4B is is like a ON indicator, it is a spare gate.
The BCD value at output of 4029 Q1-Q4, four bits, a nibble, is converted to an analog mV value across R6. The resistors R1-R4 which are connected to Q1-Q4 have weighted resistor values for the BCD 1-2-4-8. By ohms law you can understand that the analog value across R6 is approximately proportional to the BCD value. This circuit is just a single digit A-D converter, not even as good as 4 bit converter. Which means approximate value of analog at R6 will do.
Now lastly LM311 is a Comparator, it compares the Analog BCD reference at Pin-3 and the Attenuated Input signal at Pin-2. Output Pin-7 goes high when Pin-3 voltage becomes less than Pin-2. This is made to a narrow latch pulse by C2-R12-IC4C. The latch pulse freezes the BCD data to display till the next latch pulse. R8-R9 attenuate the 0-9 V DC input to a 1/100 value. The zener Diode Z1 is for protection.
I guess the LM311 circuit should work off a single supply, but a dual supply may be required as voltage levels may be near zero. You must be able to see a staircase waveform or ramp across R6. Narrow Latch pulses at Pin-5 4511 on every ramp cycle.
Thursday, March 24, 2011
The µSCOPE - A poorman's oscilloscope
The oscilloscope is still one of the most important measurement tools of the electronic engineer. With the advent of the often very reasonably priced USB scopes, such an instrument is now within reach of every body.
Digital oscilloscope - Build a simple Inexpensive digital oscilloscope. Single channel, about 100 MSPS. RS-232 based.
xoscope is a digital oscilloscope using input from a sound card orEsounD and/or a ProbeScope/osziFOX and will soon support Bitscopehardware. Includes 8 signal displays, variable time scale, math,memory, measurements, and file save/load.
xoscope - digital oscilloscope for Linux
MHZ100Q is a low cost FPGA-based high speed data acquisition system. Version 2 is a standalone board containing 2, 100MHz 8-bit A/D channels, preamp, 7th order elliptical antialiasing filters, and a Xilinx FPGA.
MHZ100Q - Open Source FPGA-based 100MHz A/D
A USB interface is implemented in the FPGA firmware. Power comes from the USB bus. Schematics, VHDL and Verilog source code, and signal capture and display software are available and being posted.
Thursday, October 09, 2008
FPGA based 16 channel 200MHz / 32 channel 100MHz logic analyzer sump.org
The project includes the actual analyzer in VHDL (for Spartan 3 FPGA) and a PC Software for the end user. The design employs a FPGA board that can be obtained easily.
- 16 channels at 200MHz sampling rate
- 32 channels up to 100MHz sampling rate
- state analysis up to 50MHz using external clock
- connects via EIA232/RS232 (works with usb to serial adapters)
100Mhz frequency counter and timer - Hardware, AVR, ATmega, ASM, Electronics, HF
In counter mode it provides 1Hz resolution up to 100Mhz. In timer mode maximum resolution is 0.0000001 Hz up to 1Hz. Resolution is reduced by one digit for each additional decade. Multiple frequency updates per second by employing a sliding window for calculation.
Wednesday, August 06, 2008
PCB Design Tutorial - As published in Silicon Chip magazine Oct-Dec 2003. A very comprehensive three part tutorial on how to professionally design and lay out PCBs. Learn all the tricks of the trade! A ground breaking article.
10MHz DDS Function Generator - A very low cost 1Hz to 10MHz sine/square function generator using a novel "sliding window" display. Based on the Analog Devices AD9835 DDS chip.
Low Cost 20MHz Function Generator - A 20MHz+ Sine/Square/Triangle function generator based on the Maxim MAX038 chip.
PC Based Digital Storage Oscilloscope Adaptor- A simple and low cost PC Based digital storage scope using a novel architecture.
FSM Compiler Based PLC- A simple and low cost Programmable logic controller based on the Finite State Machine concept. Complete with custom compiler software and source code.