delabs Circuits

Showing posts with label Logic-Circuits. Show all posts
Showing posts with label Logic-Circuits. Show all posts

Wednesday, February 08, 2017

RS Latch Erroneously setting by Itself

I am having trouble preventing my rs latch from erroneously setting. The circuit is a voltage threshold detection circuit with a nand gate whose output is tied to a SR latch.

I have capacitors across the VDC and ground for the chips and I verified the power supply's input is fairly stable. As further troubleshooting I probed with a oscilloscope at the SR latch's input and looked for anything above 1 V. The voltage never moved above 1V, but the latch still set.

I was able to place a .3 uF capacitor from the SR latch's input to ground and this seemed to fix the problem. However, it does not explain what is causing the latch to set. Any ideas or suggestions would be much appreciated. Thanks.

Some info:
Nand gate: SN74LS30
SR Latch: CD4043B
Supply to ic's is 5V from a LM7805 (with .1uF cap's across input/output)
Voltage threshold detection coming from LM339 comparator

Basic idea:
Vin ----------> |LM339 pin 4| -> |nand gate| -> |SR latch| -> |(relay driver circuit)|
Vthreshold -> |LM339 pin 5|

Mail from SM

If the power supply is stable and you do not have ground loops then that is not the problem.

If a relay or LED or some output is being driven, the current pulse may be triggering the circuit. Isolate Grounds of Loads even LEDs and Relays, Ensure EMI-RFI immunity.

RS Latch Erroneously setting by Itself

Flip-flop (electronics)

Use a 400MHz Scope and set timebase to uS-nS and see if a Spike is causing the trigger. Set the brightness level a bit high and look as close as you can.

Even a IC consuming a little extra power for a mS can set up a spike in the rail. Keep power and signal circuits on different PCBs when designing.

Check the environment and mains wiring, It could be a Laser Printer sharing the mains. If a Loose contact is present in mains box then your test circuit links with printer. Finally a good earth or ground is a must, if the unit is to operate on mains.

In the LM339 comparator use a Hysteresis Resistor feedback of 10M or 1M, Also a small cap can be placed across 10M, like 10nF if the system is a slow response one. Ensure you do not put a cap in a way to cause oscillations. A RC at input of LM339 may help.

Finally a LM339 output may have to go thru a schmitt nand buffer like 4093. to Clean the signal. Interface from a LM339 may be good with CMOS and not TTL, so a Scmitt can be tried. Nand gate: SN74LS30 and SR Latch: CD4043B seem to be different families. Use the 74HCT30 and 74HCT4043, use any one single family in Logic.

delabs

One thing i left out, The power on Start of the circuits must be defined. So a power on Set or Reset Cap with a pullup has to be provided if it is triggered by a Low. If you use a Latch which triggers by a Positive Edge then A pull down R and a Pull up Cap is required. - delabs

Tuesday, December 08, 2015

Digital Counter - 4029 and 4511

I just about the circuit you made. what kind of IC is 4029N & 4511N? Is it a diver/decoder? I tried to research on the datasheet but it cannot give exact specification...

Mail from JT from Philippines


4029 is a Preset Dec-hex, up-dn, Counter - and 4511 is a 7-Segment Display decoder. Learn more see .
Ssend a jpeg photo or rtf or pdf. please also tell me which page or circuit is this question about. any other doubts feel free to ask.

 Is it this ... Simple Digital Counter - doc00021

Digital Counter4029 and 4511

delabs


yes, .thanx for the links..i'll try to go over with the theory..so where can we purchase those items if ever we need it?

Reply from JT


It depends on which country you are in,... see this page Components Materials

delabs

Thursday, October 08, 2015

Usage of Schmitt trigger NAND Gates

I have a question about your "Long Duration Timer" circuit, del20017 found here ..Long Duration Timer Clock

Long Duration Timer


You have labeled U1 as a 4093. A 4093 is a NAND with schmitt trigger inputs, yet the schematic displays only NAND gates without schmitt trigger inputs. Which device did you intend? A 4093 or a 4011 (Quad 2 input NAND gate).

Mail from PB


Where mixed signals are at input both analog and digital 4093 is better. Like digital inputs after going thru a long cable the square wave gets deformed, 4093 refines it to a digital square again. When interfacing with input devices like switches 4093 is better as it works as a noise filter. Generally 4093(++) is an upgrade to 4011, i think it is a pin to pin replacement .

Digital Timers Counters and Clocks

In the circuit above U1C and U1D have to be schmitt trigger nands. U1B also needs a bit of wave cleaning. U1A can be 4011.

delabs


The 4093 gate didn't embed properly .. so I have attached it this time. thankyou for your prompt reply. I understand the need for schmitt triggered inputs as you have pointed out. I guess for completeness I was also pointing out that the schematic should show the NAND gates with schmitt triggers as shown below.

2 input NAND with schmitt trigger 4093.

Reply from PB


Monday, September 14, 2015

Dynamic Digital Tutors

Date: Wed, 30 May 2007 17:00:46 -0400   - Subject: 555 simulator

Hello,

I just found and had a chance to play with the 555 simulator over the internet. As I do a lot of designing and use the 555 in many of my projects, this tester is a really handy tool.

Is there a way to get a copy of this simulator that will simply run on Windows? If not, how about running it through Internet Explorer?

I realize I could simply put a link to your site and use it that way, but I don't always have a connection to the internet. Basically, I would just like to use this little applet on my laptop on my bench at home.

Thanks for your help, and congratulations on such a cool program.

Mail from DN Canada

I am happy you found my gadgets fun to use. ,

555 Oscillator and Decade Counter -Red Button Powers LED Running Lights, Adjust R2, Move Mouse over the Images.

Astable Multivibrator with 555 - Red Button Powers, Move Mouse over objects to know.

Preset Digital BCD Counter - Move Mouse over the Images, Tool Tips will Tell All.


Dynamic Digital Tutors

In the links above, you will find a code to add to your webpage or blog. I have sent you a gmail invite get a gmail then use that login to open a blogger.com account.

You ought to have a blog, these gadgets (code) can be added to your own blog, then you can refer it at your own pages. You can then share your learning with your friends too.

If you still want you use it offline let me know, i will make a zip and send it to use without internet. Have you tried using a Wireless LAN.

Wireless LAN - Wiki- A wireless LAN or WLAN is a wireless local area network, which is the linking of two or more computers without using wires. WLAN utilizes spread-spectrum or ..

Then lastly ... check these freeware you can download for 555

555 Timer PRO provides an array of design wizards, circuit blocks and information panels that facilitate the use of the 555 timer. Component value calculations for the 555 take into account the supply voltage, timer fabrication (CMOS or Bipolar), and, where appropriate, load currents.
(use the freeware version)

555 Timer Project Design Software for Beginners and Experts

Let me know if you need anything more.

delabs


Hello again,

Thanks for your quick reply. As I don't have a website nor a blog, I was hoping that the 555 program could be just a stand-alone application. Is this possible?

Your program is really nice, so I hope it can run as a small program by itself.

Reply from DN

Here is a file that will work in your laptop without internet. Can you please verify if all the three work well. digital-tutor.chm - right click - save as - to a folder of your chose and then open it (removed)

Please check both online and laptop without internet. Your feedback will be useful to me so that i can correct or improve.

delabs

See the Complete - 555 Timer at EEMetric

Saturday, April 26, 2014

Seven Segment LED display

how is the circuit for driving a seven segment led

mail from EA

A 7 segment LED display is used to display a number 0-9 using 7 LEDs, The circuit you design must have a BCD output, BCD means Binary coded decimal for number 0 it is 0000 and for number 9 it is 1001 see this chart i put in my site....  Electrical Tables

the BCD is fed to a BCD to 7 segment decoder like CD4511 or 7447 which has the logic to take care to drive your display, the displays are two types common anode and common cathode you have choose a driver to match your display, you will need to use current limiting resistors for every LED to limit current to 15mA or less. there are many circuits in my website which has examples of these.

you can also drive such displays with 7107 or 7135 to display analog signals, or with a microcontroller like 8051 using software decoding, even such examples and code is available at my website.Digital-Circuits. and Logic-Circuits.

delabs

I made an online tutorial for seven segment LED. Hope it helps you learn more.

Digital up down BCD counter "Simple Digital up down counter CD4029, with interactive javascript simulation." You can run the circuit online and try out without wiring it up.

Digital up down BCD counter
delabs


Thursday, September 08, 2005

Fuzzy Logic Links

please if you have some materials on Fuzzy logic control kindly send them to me. Thanks.

mail from MA


some fuzzy logic control links.

aptronix.com/fide/whyfuzzy.htm

fuzzy-logic.com/Ch1.htm

intel.com/design/mcs96/papers/esc_196.htm

mech.gla.ac.uk/Research/Control/activity/subsection2_3_6_6.html

omega.com/techref/fuzzylogic.html

iau.dtu.dk/~jj/pubs/logic.pdf PDF

delabs