Questions tagged [ttl]

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

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1answer
51 views

What happens if the output of a 74LS05 IC is connected to the input of a 74LS04 IC?

Explain what would happen if I connected the two ICs?
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Multisim Circuit with Virtual Crystal and TTL gates

I have to make the following circuit in Multisim: This is what I have done: As you can see, the output (in points ~Q and Q) is 0V and I can't figure out why. Could anybody help me?
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55 views

Interfacing 24VDC output with 5V TTL input

I have a project which requires me to interface a 24VDC output module (PLC) with a rather outdated 5V TTL input module. From the schematics of the old module I can draw the conclusion that it uses +...
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71 views

Understanding Resistor Values in TTL NOT Gate

I've been teaching myself electronics and a current approach I am taking, is to be able to describe the purpose of every element in the standard TTL NOT gate: Circuit lab TTL NOT Gate At this point ...
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37 views

Connecting flowmeter via USB to a computer

I have a Swiss flowmeter sf800 which generates 5v pulses if liquid passes through it. I want to connect it to a computer and count pulses via USB. I realize that I need some kind of converter to do so....
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62 views

XOR Gate implemented with BC547 transistors not working

I have checked and rechecked the wiring on my breadboard against the circuit shown in the schematic a dozen times and can't for the life of me understand why it is not working. Can anyone see a fault ...
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1answer
102 views

TTL Logic Gate Resistor Values

I've been teaching myself the basics of circuits for the last few months and have been enjoying going into chip schematics. I'm trying to understand why the resistor values are as they are. For ...
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2answers
57 views

Mux UART with 74xx Multiplexer

I have a legacy LPC MCU with 2 UARTs only. One of these UARTs is reserved for different functions such as IAP and RS232. So basically, I have one UART available only. For an experimental project I ...
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2answers
127 views

Raspberry Pi with 74HC14 connecting to LED strip (WS2812B)

This might be a stupid question, but I can't seem to figure out how to convert 3.3V to 5V with the 74HC14. I have a power source which can supply 5V (see the power adapter at the left), and use it to ...
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1answer
696 views

pull-ups between logic gates

I'm trying to understand why, on this circuit bit, they used pull-ups resistors between logic ICs of the 74LS and CD4000 families. Specifically I'm talking about resistor array RM1 and R1. All the ICs ...
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58 views

Can you effectively run lower power 5V TTL signals through a large piece of metal?

Is it possible to run a standard TTL signal through a very large piece of metal? For example, say 1-3 meters of metallic rebar?
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TTL “radio-button” using priority encoder and latch

I'm liking this site and I am not always using it to just throw a question but to develop ideas all the way. First time I did that was on StackOverflow I need JSZip and gzip for my web page, and JSZip ...
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Are there combo gates XOR followed by AND? (4-bit identity comparator)

Is there no 4 bit identity comparator in TTL or CMOS? It could fit into a DIP-12 package as all it would have is 4 XOR gates for selectable invesion and 1 4-way AND gate. OUT := (A1 xor B1) and (A2 ...
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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 ...
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2answers
196 views

Is this circuit from a textbook wrong?

(This is not a homework question.) While reading "Digital Computer Electronics" by Albert P. Malvino, I found this circuit on page 121, figure 8-22(a). It claims to be an example of a discrete TTL ...
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how to calculate vb1 and vo in this TTL circuit?

By referring to question (i) how to calculate Vb1 and Vo? can i assume Vb1=Vbe(sat) and Vo=5v?
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1answer
60 views

Implement boolean expression with AOI

Below is a question in my homework: \$F(P,Q,R,S,T)=(P+Q)S+(R+T)\bar S\$ using one or more 2x2 AOI."> Here's my attempt for (a): Step 1: simplify boolean expression. \$F(P,Q,R,S,T)\$ \$=(...
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Why does adding this low pass-filter to a monostable multivibrator prevent triggering?

A 24 VDC sinking sensor is tied to an SSR. The SSR converts the signal from 24 VDC to 5 VDC. The output of the SSR goes directly to input B of a 74121 One-shot. (The diagram has a resistor and ...
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1answer
80 views

1 TTL IC -> inverter + 2-input NAND + 3-input NAND

I came across this question in my homework: Implement the following gates using only one TTL IC: one inverter, one 2-input NAND and one 3-input NAND. The type of IC they're talking about has 14 ...
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Reverse Feedback protection in a RC circuit

I have been working on a model CPU build from LS TTL ICs for the past couple of weeks. I am going to give a little background here, during the prototyping I stumbled upon several intresting issues ...
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1answer
221 views

Can I use a ST-LINK V2 as a universal JTAG or TTL serial interface?

I have a ST Link V2 as pictured below. I would like to use it as a general purpose JTAG and or Serial TTL USB interface for communicating with a wide variety of devices. The documentation claims it ...
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1answer
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TTL to NIM logic translation Logic Gate Issue

NIM is a standard used in nuclear physics. I'm facing an issue with a logic gate being used in my TTL to NIM translation circuit, and I'm not sure what is entirely wrong with it. For a little ...
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102 views

Can I use a cheap logic analyzer as a USB to UART TTL cable?

I need a USB to UART (TTL) cable for connecting to an onboard JTAG connector. Since I already own a Sigrok logic analyzer, I figure it might function soley as a USB to UART cable. Is this possible? ...
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54 views

TTL 10µs wide generation on CMOS rising edge?

I want to use a DG645 from Stanford research to trigg two different laser. To do this, I need four 10µs negative TTL signal. The DG645 send +5V CMOS signal (picture below). Since I have a little ...
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82 views

74LS181: Maximum output current?

It seems that I fried my 74LS181N ALU, though I'm operating on 4.95v and have a 1k resistor (plus LED) on all output pins. I was sure it could handle those 5mA, but the datasheet suggests an output ...
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59 views

Voltages at nodes in TTL logic gate

I'm trying to answer the question that has been given here. I think I understand which transistors are on and which are not under the two different logic states i and ii. However, what I really ...
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Signal conversion LVDS, RS422 and LVTTL

What are all the parameters required to LVDS to lvttl, RS422 to LVTTL and LVTTL to LVDS and RS422 signal conversion?
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Deciding between ULN2804 or ULN2803 with 74HC595

I'm making a circuit with Arduino + 74HC595 + (ULN2804 / ULN2803) to drive a few 12 V Motors. I'm trying to decide whether to use the ULN2804 or ULN2804. On testing, performance of both is fine, ...
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How to connect STM32F103C8t6 to computer when using USART? [closed]

I'm an electrical engineering student and I've just started to learn microcontrollers.I want to know is there any way to connect my board(I uploaded its picture)to computer when I'm using USART ...
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70 views

What DC Power Supply Do I Need To Get For This Device?

I recently bought a small 3 to 1 HDMI Amplifier Switcher. It can work without power adapter only if the 3 HDMI inputs are connected and supplying current. I want to operate it with only 2 input which ...
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1answer
82 views

Why cannot I use the USB port directly to communicate via PC with STM32F4-DISC

I will keep it short and clean, if it won't be enough please let me know and add more details. When using an Arduino UNO, a serial communication can be achieved by the same USB connection which is ...
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1answer
144 views

If you wire together two TTL outputs, which one wins?

If you connect together two outputs from 7400 NAND gates, which output will dominate - high or low? Background: I'm reverse-engineering a 1969 circuit board, and in multiple cases they tie together ...
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77 views

Will SN74HC245N transceiver support TTL RX when blocked?

I'm actually designing a system with: ~10 "Master" boards that transmit data from slaves boards to a RS485 network 4 "Slave" boards per master one, connected trough a 3 pin jack (5V, GND and half-...
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182 views

What's the difference between 74LS00 “gates” and 74LS37 “buffers”?

The TI 74LS00 is "quadruple 2-input positive-NAND gates" and the 74LS37 is "quadruple 2-input positive-NAND buffers." The pinouts are identical. The LCCC package is documented exactly the same for ...
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1answer
86 views

What's the phase relation between the sine wave and the sync output from a function generator?

I'm using a function generator to generate a sine wave, and am trying to use the sync (TTL) output to flash an LED at the beginning of each wave pulse. However, when I compare the sin wave and the ...
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94 views

Fundamental TTL circuit and its operation

So i am studying TTL circuits and i started with fundamental configuration as shown in the following picture. NOTE: Transistor Q1 is actually a two emitter transistor, i just couldn't find proper ...
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59 views

3.3V TTL is dropping to 2v when connected to pin [closed]

3.3V TTL is dropping to 2v when connected to pin. can i use a current limiting resistor in series to maintain 3.3v. Need suggestions.
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810 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 ...
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69 views

FT232R TTL Logic Levels

I have an FT232R chip hooked up to my oscilloscope with the TX and RX pins joined. I'm sending characters directly to it via Putty. The logic levels I am seeing are 5V low and 0V high. I thought the ...
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3answers
239 views

MAX232 Replacement

I have a circuit where a 12V square wave signal (a Profile Ignition Pickup signal from a Ford EDIS ignition module) was fed to an MCU via a MAX232 chip. My understanding of the MAX232 is that the ...
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Switch between USB and Bluetooth module TTL

In my project I have an MCU that I want to communicate with via 5V TTL serial. I have two methods of doing this in my circuit, USB via an FT232R (5V) and Bluetooth via an HC-05 module and level ...
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1answer
37 views

Pull down for 74HCTXX series logic ICs

I am building an adder with standard 74HC/HCT series logic ICs. I see the result when input pins are left floating are erroneous. Shall I have to connect some pull down resistors. Thank you.
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What specs does the “gros condo” (big capacitor) needs to have?

I have a pair of Dynaudio Air 20 at home. Unfortunately, the cable that used to control the speakers via RS232 died. I opened the cable, and saw that it was a customized RS-232 to TTL adapter, but ...
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52 views

Setting measurement points of the 74HC86 delay time

simulate this circuit – Schematic created using CircuitLab I'm measuring a propagation delay and transition delay of a 74HC86 chip. I setted somewhat high frequency square-wave signal(100kHz) ...
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121 views

Component recognition from marking code

I need help to recognize a dead component from a lab instrument control board. It is part of a TTL-serial interface, arguably a logic gate or some level shifter, in a TSSOP-14 package. You can see ...
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1answer
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Unpowered 74ls chips vs Powered Nano?

I have a power-hungry 74ls digital logic project that I want to connect a USB-connected Arduino Nano to, but I'm not sure how design the interface between them safely. The project has an external 5V ...
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2answers
138 views

Converting a variable frequency to TTL HIGH and LOW levels, based on a fixed (possible non-fixed?) frequency

I have a square output from an LM324 op-amp (0 and 5 volts) which has a frequency between 1 to 500 Hz (yes, low frequencies). I would like to find a simple way to have HIGH TTL signal when it is over ...
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1answer
148 views

Supplying TTL Signal via USB

I have two pieces of hardware I'd like to interface with via USB. The first are 2002 Series Actuated Valves and the second is a Mass-Flo Controller for regulating gas exchange. To my (admittedly ...
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4answers
152 views

TTL Logic for displaying large 7-segment values [closed]

For fun, I was trying to imagine how I might implement large values in 74 series logic (or any commonly available discrete logic from the 1970s). An example might be displaying prime numbers up to ...
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3answers
124 views

TTL square wave inverter adjustable duty cycle

I am an amateur and I don't have experience with logic circuits so please forgive me if this is very simple. I have a 5V TTL crystal oscillator (4-pin). I need to create a second square wave from it ...

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