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Questions tagged [ttl]

Transistor Transistor Logic. Logic circuits built from bipolar transistors and resistors.

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24
votes
8answers
11k views

Is it worth it learning how to use 7400 series “jelly bean” logic IC's or are they completely obsolete?

My road map for learning electronics included the 7400 series logic chips. I started in on electronics by following the labs in the "Art of Electronics" lab manual which includes labs with these chips....
24
votes
6answers
4k views

What are the advantages of using FPGAs over TTL in intro computer architecture?

I teach the one and only computer architecture course at a liberal arts college. The course is required for the computer science major and minor. We do not have computer engineering, electrical ...
20
votes
3answers
19k views

What does a two overlapping circles symbol mean in an electrical schematic/diagram?

In the datasheet for a A3503 Hall Effect Sensor, I saw a circuit diagram labeled 'Functional Block Diagram', and it shows a symbol I have not seen before. It's shown here between 3 - Output and 2 - ...
15
votes
2answers
37k views

How does TTL serial work?

I've been trying to find a good description of the TTL serial "standard" without much luck. I understand that serial transmit (TX) and receive (RX) lines idle high (at VCC) and that they drop to ...
13
votes
4answers
1k views

What logic family is best for general-purpose hobbyist stuff?

I need to buy a few logic ICs. Which family should I get? HC? HCT? Which kind is best to have lying around in a parts box, for maximum compatibility with unpredictable future projects? Wide supply ...
13
votes
1answer
4k views

How is this circuit for level converting (5V<>3.3V) working?

Does anybody know, how is this circuit exactly working? It is level converter between 5V and 3.3V logic and it is bi-directional. I have some theory, but I am not sure with it (I never worked with ...
11
votes
2answers
791 views

Does this circuit have marginal voltage level problem?

As a research for the problem I described here I found this circuit by Maxim: This is clock doubler, and must be a really good fit in my case as input frequency is very well defined. However looking ...
8
votes
4answers
3k views

Buffering a Digital Microcontroller Signal for Connecting to an Optocoupler

I frequently work on projects in which I use optocouplers for isolating digital +5VDC control signals (for example, from a microcontroller) from the rest of the circuit. However, since these work by ...
8
votes
2answers
1k views

How to manufacture chip on board?

I am a developer of a cheap product and i have no experience in mass production. Device is fully functional and represents a single sided PCB, a microcontroller, a bunch of diodes and a few passive ...
8
votes
2answers
2k views

In a 74HC14 Schmitt trigger IC, unused inputs/outpus

I have a 74HC14 Schmitt trigger IC. I only use one of the I/O pairs, and everything else is not used. I understand that in TTL logic the unused the inputs should be set to either high or low to ...
8
votes
4answers
3k views

Should I use CMOS vs. TTL?

Now, I know that this question has been asked so many times that it seems like I'm trolling, but I must point out that I couldn't find the right answer to this question anywhere. So yeah, CMOS and ...
8
votes
2answers
6k views

Interfacing Arduino to C64's tape port

Update: a practical implementation of this is done in the Tapuino project made by Peter Edwards. Check it out, everything is open sourced: https://github.com/sweetlilmre/tapuino I'm working on a ...
7
votes
1answer
10k views

How to convert a digital signal from 24V to 5V

I have an industrial automaton that gives me a digital signal (24V or 0V) on its outputs and I want this signal to control an integrated circuit, but the integrated circuit only takes a TTL signal in ...
7
votes
1answer
909 views

Capacitors in MAX 232

Out of curiosity, can I replace the electrolytic capacitors in the circuit with non-polar ceramic capacitors? Will I get the shifting in level? MAX232 datasheet: LINK
7
votes
3answers
5k views

Connecting unused logic gates

Logic gates like AND, OR, NOT etc. often come packed as arrays in ICs. Sometimes not all gates are used in a project. I would like to know how the remaining unused gates should be connected to ...
7
votes
1answer
10k views

TTL voltage shift from 5 to 3.3 Volts “UART”

I want to make serial communication with a device which works on 0-5 Volt TTL level. But my serial chip uses 3.3 Volt logic. (this is an UART communication) I know that I need a step down at least ...
7
votes
2answers
980 views

What should be considered when sizing trace widths for digital logic signals?

For traces that carry a static DC current, it's pretty easy to calculate the minimum trace width based on the required ampacity of the trace. However, I'm not sure what should be considered when ...
6
votes
3answers
11k views

Bidirectional level swiching 5V <-> 3.3V

I am looking to interface a 3.3V device with a 5V one. This will require the shifting of the logic levels between the two devices. Doing this in one direction is a trivial matter, but I need to do ...
6
votes
1answer
3k views

Should I calculate a resistor value for driving indicator LEDs from TTL outputs?

Traditionally I have always used a \$1\:\mathrm{k\Omega}\$ resistor as a current limiting resistor for driving an LED direct from a TTL (or 5V CMOS) output. I can't remember how I came by this value -...
6
votes
4answers
19k views

Rising edge pulse detector from logic gates

The circuits I describe are entirely made of 7400 series logic gates (7402, 7404 and 7408 ic). I'm trying to build a rising (positive) edge pulse detector using logic gates. The following circuit ...
6
votes
2answers
360 views

limit duration 1pps signal

As a beginner in electronics, I would appreciate very much to get some input from you folks for my project, so I can decide in what direction to point my nose :) What would I like to do? I would ...
5
votes
3answers
2k views

Going from Transistors to Gates to…IC's?

So I am trying to understand I guess what is probably a basic concept of computers. I was taking a look at this previous question: From Transistor to Gates And it's accompanying link: http://www.cs....
5
votes
3answers
1k views

Looking for a device to “pass through” or “make high impedance” 8 bits based on one control bit

I need a thing (preferably a single IC) that has 8-bit input, 8-bit output and a control bit, with this behaviour: If the control bit is active, set output bits to the inputs (no need to actually ...
5
votes
5answers
1k views

Why do TTL pulse generators generate an asymmetrical square wave (unlike CMOS)?

I've read that the asymmetrical (about 1/3 mark-to-space) output waveform is due to input gate characteristics of a TTL inverter, but I want to know more about which characteristics of the TTL input ...
5
votes
3answers
1k views

IC takes no input (or high) as high and low input as low on breadboard

I was working with IC 7400 (or LM74LS00 / NAND) (and IC 7486 - XOR) to design and verify combination circuits and logic gates. Consider the lower end of breadboard as LOW (connected to GROUND) and ...
5
votes
2answers
2k views

CMOS vs TTL Logic Gates?

This is probably a simple question but how come CMOS Logic Gates built from Only Transistors is completely different from one that uses TTL Logic (Like BJT's). I know BJT aren't really used anymore ...
5
votes
3answers
3k views

Which logic gate family is used in a PC? TTL or CMOS?

I read that the propagation delay of CMOS logic gate is longer than TTL; therefore they are not used where speed of processing is important. I thought computers or computer cpu is using CMOS. ...
5
votes
4answers
5k views

Switching relay with a PNP and TTL levels

I can not wrap my head around the fact how I can drive a relay (24V, 160ohm) with an tip32a PNP transistor which has TTL inputs from a controller. I can easily calculate my resistors when I use the ...
5
votes
1answer
2k views

What to do with unused TTL and CMOS outputs?

Just about everything I've read on the Web, including on this site, say that unused TTL and CMOS outputs should be left floating. However, this TI article, Designing with Logic, states: Unused ...
5
votes
2answers
2k views

CMOS (or CMOS compatible) shift register with latched open-drain outputs

I've been looking for a 3.3V compatible shift register (SIPO) with latched open-drain outputs. I've settled on a 74xx596 (not a '595!), but of all the 74xx CMOS series I've been looking at omit this ...
5
votes
4answers
1k views

Can I connect TTL gates directly to the address bus of a Z80 CPU?

I need to know when the 14 MSB bits from the address bus of a z80 CPU are high. To do so my first idea is to use 4 74LS08 ICs (TTL AND gates) reading those lines but I don't know the maximum amount of ...
5
votes
3answers
2k views

Driving LEDs / other small loads with a 74HC06 or similar inverter

I was recently reverse-engineering some firmware (and other bits) from a router, and spotted that the front panel LEDs were driven from a 74HC06 hex inverter gate chip rather than a proper LED driver. ...
5
votes
2answers
272 views

current limiting resistors

I notice that in Ben Eaters project for the 74 series logic chip computer, which my son and I are building, sometimes he uses current limiting resistors on LED's on the pins of some chips, and on ...
5
votes
1answer
505 views

Dual power supply confusing TTL serial?

Sorry for the vague title: I'm a bit of a noob at analogue electronics, more a logic &software guy. Basic problem is I'm sitting at the end of a cable with a USB powered Arduino trying to send ...
5
votes
2answers
2k views

How to detect Serial or TTL signal for a PIC?

I have a Microchip PIC with UART support. If i understand correctly, the UART is able to natively handle the TTL serial signal. I'm expecting input signal that should be TTL (0/5V), but it could be ...
4
votes
1answer
2k views

7405 TTL Chip outputting nothing when given low input

I’m struggling learning how to use some of these components for a lab. One thing I noticed is that when giving the 7405 hex inverter a low input, the output when checked by my logic probe shows there’...
4
votes
6answers
2k views

Multiplexing UART

I'd like to interface my main microcontroller's hardware serial port to more than one device at the same time. My understanding is that UART on my microcontrollers is based on an active-low 5V TTL. (...
4
votes
3answers
958 views

How to build a noise generator based entirely on logic gates?

I would like to build a noise generator based on logic gates. It could be white noise generator or a random bits generator that sound similar to a noise source. I need a circuit recommendation or an ...
4
votes
3answers
465 views

Using HC/HCT, AHC/AHCT series logic

I am builing a circuit, and i need to connect a few different IC's (obiosly). My circuit is based on 5V TTL logic and i found a part that is made only in AHC/AHCT variant. So let's take it from the ...
4
votes
2answers
2k views

How to convert sine wave from an oscillator to TTL signal for microcontroller?

I tried to measure inductance by using a colpitts oscillator to generate sine wave. It works. I need to convert the sine wave to 5V square wave to feed to a microprocessor. The sine wave is coupled ...
4
votes
3answers
1k views

IC chips and datasheets

I'm still just beginning my adventure into electronics and IC chips and datasheets have me confused so I'm going to ask a series of beginner questions will help me and hopefully others as well. There ...
4
votes
1answer
2k views

Is interfacing the 5V TTL UART with 3.3V microcontroller via voltage divider possible?

I need to connect my MSP430 microcontroller (3.3V) to interact with a 5V TTL UART camera (http://www.cn-lcf.net/sdp/561974/4/pd-2909996/7575433-2127043/LCF-23M_OV528_Protocol_RS232_Camera_Module.html)....
4
votes
2answers
904 views

Interfacing 3V TI MSP430 to PC serial port

I am scratching my head to figure out a possible soloution for this scenario: I am developing a simple application using TI MSP430 microcontroller. The microcontrol part is powered by 2xAA batteries. ...
4
votes
2answers
832 views

Driving 74HC logic with sub-nano second clock reference

My goal: I am trying to phase lock a 74HC-based digital circuit from a clock reference at 10~15MHz pulse repetition rate. The pulse width is around 400 picosecond. The peak voltage is sometimes below ...
4
votes
1answer
10k views

Is it possible to program an STM32 with an Arduino?

I have one of these: http://www.ebay.com/itm/111297094334?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 I know an USB-TLL dongle is usually used to program it, but I don't have one and I ...
4
votes
1answer
175 views

Why are bipolar transistors often used with the base at vcc?

I often find transistors used as shown below. Note that the BJT to the left is being used in a strange configuration, where the base is being pulled permanently high. What on earth is the transistor ...
4
votes
1answer
3k views

Increase 74LS TTL gate's output current to drive multiple high-power LEDs

If have several 1 watt LEDs that I want to drive off of a TTL gate's ouput. What can I do to increase a 74LS TTL logic chip's output fan-out (current) to be able to produce a true 5 V output that is ...
4
votes
1answer
1k views

TTL logical low isn't ground

I'm working with an Arduino Due and four 5V TTL pressure sensors. I'm using this logic level converter to convert from the 3.3V Due to the 5V sensors. I've been having problems using all four at a ...
3
votes
4answers
2k views

Purpose of pullup resistor in BJT LED driver circuit

One answer to this question suggests the following circuit to drive a LED from an open collector output of a 74LS47: simulate this circuit – Schematic created using CircuitLab What is the ...
3
votes
2answers
487 views

Why is my XNOR output always low?

I recently bought some Texas Instruments TTL chips. So far they've been OK, except the XNOR (SN74HC266N) chips (I've tried 3, including one that's never been in my "real" circuit) always output low ...