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Tuesday, January 29, 2019

Mixed Signal Grounding Method

How do we interface Analog and Digital Blocks. The earlier post explains ground connections that are radiating from supply but does not show Analog and Digital Blocks Interface.



Analog Blocks have Opamps, Analog Mux, A/D Convertors and D/A Convertors. Some microcontrollers have built in A/D and D/A then you have to use the separate ground pins they provide. The implementation remains the same.

Mixed Signal Grounding Method

The diagram above is self explanatory. There are mainly types of return ground paths... to the power supply ground

Pulsing Ground - From Digital circuits that are switching in MHz speeds.
High Current Ground - From Interface or Power, LED, Motor Circuits.
Clean Signal Ground - From Analog Signal Conditioning and Mixed Signal.

Use proper decoupling caps at every chip and every functional circuit block. Have a ground plane that doubles up as a shield in on or more layers of PCB. In RF circuits you could use two ground planes on two layers of pcb and signal tracks in between.

Wednesday, January 16, 2019

LM3914 Circuit Ground Connections

I am about to build the circuit that you have here: - Millivolt Meter - Bargraph

I am pretty sure that I understand all of it, except for the symbols that you have at the grounds which are little triangles with the letter F next to them. Please excuse my ignorance, but what does that mean? Is that the ground from the tested millivolt source?

MK


One Ground carries the LED Currents and that track has to be thick and go directly to the Voltage Regulator 7805 which provides 5V supply. If this track is looped with the signal ground, millivolts of error may occur in reading and if tracks are thin it may lead to oscillations.

LM3914 Circuit Ground Connections

We have a High Gain Amp  in this circuit that will amplify even these small jumps in mV due to track Resistance in ground loops.

Analog Ground, Digital Ground, Supply Ground, RF Ground and Earthing have to be carefully designed to get accurate performance. PCB Autorouting may ignore these subtle requirements.

Monday, January 14, 2019

ICL7135 PCB Layout Method

I have design a PCB layout for a 4.5 digit voltmeter using the ICL7135 chip, and i have problems with the analog and digital ground. Do you know if somebody have make a PCB for this chip?

I have seen in your schematic a superb circuit- del2003.sch, ICL7135 based auto ranging DVM. Do you know if the PCB layout is avalaible?

I will appreciate to have some help or if someone can send me the PCB layout for the del2003.sch.
Thanking you in advance,

Mail from RL


I am not able to locate my PCB Layouts, but to study about analog and digital grounds for this chip and pcb layout see this Service Manual i found online.

delabs Notes -  Discuss Topic here EE Forum - Analog Ground

Digital Grounds have Switching Noise or Pulses, Interface Grounds have higher currents. Sensor  Low inputs that are not isolated may have potentials and may lift the system ground and also pose hazard. Electrical Earthing and System Grounding are also different things.

Analog Ground and Digital Ground

Keep the analog and digital current return paths separated.  Remember all tracks and wires are resistors and conductors too. connectors have contact resistance. soldered joints (and connectors) have thermometric EMF. Looping Tracks is wrong Radiating tracks is right.

Read this PDF too Grounding in mixed-signal systems demystified, Part 1
Undoubtedly, grounding is one of the most discussed subjects in system design. Though the basic concepts are relatively simple, the implementation is difficult. For linear systems, the ground is the reference against which the signal is based; and, unfortunately,

Wednesday, February 28, 2018

DC Small Motor Control using PWM

message: Greetings, I have a kit motor controller. I works just fine. It uses the NE556. I read some where ( on a NE555 )that I can change one of the capacitors with a variable capacitor to get the full range of frequencies out of the NE555.

 Is it possible to get adjustable frequencies out of the NE556? I have the circuit drawing. Is there any one I can send the diagram to so they could tell me which capacitor I can change? Thank you,

BR USA


PWM DC Motor Speed Control - This is a circuit for controlling the speed of small DC motors, it works nicely as a speed controller for an HO or N gauge model railroad.

DC Motor Control for Low Power

Timing 555 Motor Speed - It uses a variable frequency 555 astable. The astable triggers a monostable that produces pulses of a fixed width. At lower frequencies, the monostable pulses are infrequent and the output is high about 20% of the time.

delabs

Isolation Resistance and Insulation Resistance

message: what is insulation and isolation resistance, why and how it is measured? what are the consequences if it is not measured? 2008


Isolation Resistance and Insulation Resistance are both related to each other. Isolation Resistance could be in Giga Ohms and Tera Ohms and includes Surface Resistivity.

Insulation Resistance will be in the Range of Mega Ohms and Giga Ohms. You could say Isolation Resistance is a Tera Ohm and Giga Ohm Measurement Test.

Isolation Resistance and Insulation Resistance

Les us assume a 5KV Isolation Opto-Coupler on a Glass Epoxy PCB. You could Measure its Isolation or Insulation Resistance and it will be in the range of 1 Tera Ohms in a good PCB.

A good PCB will have a Slot Routed below the Opto Coupler for High Isolation. This will ensure Dust and Grime along with Moisture will not form a Leakage path below opto-coupler.

Use a Megohmmeter for Insulation Resistance of Transformers, Coils and Relays. Use a Teraohm Meter to measure Isolation Resistance in Opto Couplers, PCB, Ceramics and Capacitors.

Megohmmeter is a special type of ohmmeter used to measure the electrical resistance of insulators. Insulating components, for example cable jackets, must be tested for their insulation strength at the time of commissioning and as part of maintenance of high voltage electrical equipment and installations.

6520 Programmable Teraohmmeter makes resistance measurements up to 10 PΩ. Whether used in automated mode via the Guildline developed TeraCal Software or as a stand-alone meter,

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