Sample and Hold with Standby CD4053

A, B, and C are the Digital Control for x, y and z input and output pairs.The voltage at Vinx is stored in C1 when A goes high, when A is low the voltage stored in C1 is read by buffer U2A.

It could be used in DMM circuits as Analog Memory DMM range, AC-DC mode, logic control

Sample and Hold with Standby CD4053

Another application of  Mux 8 Channel 4-20mA Analog Multiplexer

The stby or standby input should be low when sample and hold is operating. If stby is taken high then C1 Cap is isolated and leakage is minimum. The supply of +/- 7.5V is chosen as OFF resistance of 4053 is high at this supply.

Interface a uC to PC RS232 with MAX232A

This is the standard configuration on how to Interface a uC like 8051 to PC RS232 with MAX232A. The UART or Serial port was not present in 8049/8749 chips which were the ancestors of 8051/8031. Pages of code were needed to make a software UART in MCS-48. The 8051 integrated the hardware UART and short commands made it tick. The most important innovation which made uC popular was the C in 80C31. C is for CMOS. This made the chip work cooler and work on even batteries and small power supplies.

80C51, SBC, Firmware and Circuits

The 8749 and 8751 are the UV EPROM type of uC. With limited erase/write cycles. The FLASH revolution changed every thing, you could update firmware over a phone line modem. Even without Ethernet, the firmware could be updated by making every embedded device a node on the EPABX. Now TCP/IP and Wi-Fi makes it all very easy.

Interface a uC to PC RS232 with MAX232A
Read also –

Simple Sample and Hold with CD4066

A sample and hold is like an analog memory. If The digital control A is low 4066 switch is open, and when A is high switch is closed. U2B is a buffer so as to ensure quick charging of C1 thru 4066 on resistance of 100E.

Simple Sample and Hold with CD4066

Mixed and Interface Circuits

U2A is a FET input opamp buffer which does not load or drain the cap C1. When A goes high the input analog sample is stored in C1. A has to be high for say 10*1uF*100E = 1mS, so that a proper stable sample is stored. When A is low C1 undergoes very slow discharge as opamp input resistance and 4066 off resistance is in giga ohms. The accuracy of reading Vout falls with respect to time due to leakage currents.

Edison Bulb Life Extender

The Edsion Filament lamp may be less popular, but it is the most cost-effective light even today. It is very affordable, The light is soothing to the eyes and best of all gives a warm feeling.

Edison Bulb Life Extender

Sometimes due to the mains being restored when bulb is on, or a rapid flick of switch, blows it. This may be due to the cold filament resistance which is low, allowing a huge inrush current.

LED Lighting – The Future is Here

The problem can be solved with a soft start based on thyristor or mosfet using PWM etc. The circuit here is a low cost solution which may help a bit in reducing the inrush cold current Protection from long duration high voltages is also required but will make circuit more complex.

Now why would anyone spend for a R-C network for a bulb, you could as well buy a new bulb. But I once got a back sprain while replacing a bulb in a hurry, So the price of the bulb alone is not the issue.

CFL Lamps and Simple Inverter

The two diodes 1A form a AC path with a switching delay of diodes, The R-C network is for soft start. The Varistor-Thermistor has a cold resistance 4.7E which reduces as it warms up. If switch is flicked rapidly or power fluctuates, then varistor cannot help as its response is slow. The 10E resistor ceramic fusible wirewound resistor and C1 does the job of absorbing .

This circuit has not been tested for long times at multiple places, so i am not sure of its performance.

Microohm Meter with LED Analog Bar

This indicates like LM3914 in dot-mode. It is a drawing i made made to troubleshoot a gadget, around two decades ago. Strangely it had a echo of a design i had made into a 7107 dpm years before that. Now i am scanning all my drawing and notes, useful or not. Clean or with errors. Many Errors = 1 Blunder. Some projects i made have been expensive Blunders. So see them with a skeptic eye, fix them, try them. Thats all for now.

See the Circuit Full Size – Microohm Meter with LED Analog Bar

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.

Interface ICL7135 Voltmeter to PC

A PC based Analog Voltmeter. The Printer Port or Parallel Port Interface is used to acquire high resolution analog data using ICL7135. This is a method of getting analog data into your PC. This is only of Educational Value. Applications include Data Loggers and PC based Process Monitors, chart recorders. (USB, Wireless Interfaces and Tablet Computers are in vogue today

ICL7135 to Printer port Interface

The four Digit Drive outputs and four BCD outputs of the Multiplexed Display Driver of 7135, along with A-D status output which is also four, are routed to four input pins on printer port via three 74HCT373 Digital Switches. This is because we have less Input pins on Port and 4 are shared by making one 74HCT373 transparent and others High Impedance when PC takes a reading. So the three sets of four outputs of 7135 can be read sequentially.

ICL7135 to Printer port Interface

74HCT139 U9A which is controlled by the PC program can select U3, U4 or U5 for sending data to 4 pins on printer port. Data sent on the eight output pins of printer port can be latched by U10B into U6. This eight outputs of U6 can drive relays or lamps.

The ICL7135 details can be seen here 41/2 A/D with BCD ICL7135 . This Mixed device was far ahead of its times, a product of Intersil.

AD590 based Temperature Sensor

Learn how to use the AD590 to measure environment temperatures for display, logging or cold junction compensation.

The voltage at the point 1 of R4 will be :Vo=( 1+ ( 10K/22K)) * Vref = 3.63V as nominal Vref is
2.5V.AD590 is a current source which gives 1 uA / kelvin, It is independent of the voltage across the device. you can treat it like a current source or sink or impedance. total voltage across AD590 is 5V as opamp pin 2 is at virtual ground.

Analog Circuits – OpAmp, Signal Condition, Mixed Signal.

AD590 based Temperature Sensor

This is the way you try to understand the design.

The AD590, here is a constant current sink as cathode goes to -5. The current it sucks away or drains from node pin 2 of OP07 is 1uA/ kelvin. at 0 deg C the current drained is 273 uA at 26 deg C it is 300uA.

You know according to theory that the amount of current entering the node, is equal to the amount of current leaving the node. do not look at voltages now, look at the currents. the AD590 drinks 273uA from Node pin 2 of OP07 at 0 deg C. Now no current can come from opamp OP07 pin 2 as resistance is in giga ohms and leakage in pico amps. now the pot R5 and resistor R4 are just in series and connected to 3.63 V as established earlier. The TL431 is a shunt regulator with reference and has a low impedence. Now the R5 + R4 combination should not load the TL431, that is not the case as 3.6 / 10K = 360uA .

By varying R5 pot you can pump 3.6 / 10K = 360uA down to 130uA when R5 is max into node pin 2 of OP07. This pot will be calibrated with AD590 in ICE to give a 0 mV output of the Op07. When calibrated R5+R4 pump 273 uA into node pin 2 of op07. this is sucked away by the AD590 which is draining 273uA at 0 deg C. This leaves the pin 2 at zero potential as currents leaving = currents entering.

Now to understand the opamp functioning.

The pin 2 of opamp is a 0 potential as calculated above and pin 3 also is at zero pulled down by R7. Now as both inputs are at same potential the output of opamp also is zero. The feedback resistors R1 and R2 will carry no current as both their ends are at 0. the Vout is now 0 mV and AD590 is on a block of ICE and opamp is stable.

If pin 2 (-) becomes more dominant or positive than pin 3 (+) the output swings negative. If pin 3 (+) becomes more dominant or positive than pin 2 (-) the output swings positive. The opamp on feedback tries to maintain both the inputs at the same potential. This thumb rule can be used to make opamp oscillate, amplify or compute.

Now what happens when the AD590 is removed from the block of ICE. It comes to room temperature say 26 deg C which means 300uA. Now the AD590 demands to draw 300uA from node pin 2 of OP07. The R4 + R5 from 3.6 V can give 273uA as it is fixed, not a uA more. The rest which is 300 – 273 = 27uA leads to a drop in potential at pin 2 and it turns negative. as demand is greater than supply. which makes pin 3 which is at zero more positive than pin 2. ( theory : 0 is positive compared to -1) as pin 3 is more dominant opamp swings positive as per thumb rule. and a current starts flowing thru R1 + R2 till the current reaches 27uA. at this point the extra current 27uA drawn by AD590 is supplied by opamp thru R1+R2. The Pin 2 now comes to 0 as currents leaving = currents entering.

Test & Measurement, Instrumentation

At this point the voltage at opamp output is given by ( R1 + R2 ) * 27uA = 270mV (assume R1+R2 is 10K after calibration) now opamp gives 10mV per deg C.as opamp now is a closed loop control the rise and fall in temperature, results in AD590 current variation which produces a proportional OP07 output.

Now the explanation above is in steps but all that happens in real time in an instant.