# Questions tagged [ttl]

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

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53 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 ...
90 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 ...
75 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 ...
8k views

### TTL NAND gate (totem pole) current and voltage analysis

I am working on a few practice problems for my course and I am unsure about my working throughout. hoping for some feedback and guidance from the community as it's not my strongest topic. Here is ...
50 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 ...
397 views

### TTL gate function

Can you explain the logic function of this TTL gate? I think it is $$Y = \overline{AB+CD} \$$ but I am not sure. If $$V_1=5V \\ V_2=0V$$ does the transistor Q1 work in reverse-active mode?
407 views

### Problem with testing 74ls173AN D flip-flop

I'm building a simple 4-bit computer (a Nibbler) from 74 series ICs on a breadboard. Right now I'm working on 74LS173AN IC registers. I can't make it work. I have connected the input enable (pin 9,10),...
511 views

### VHDL: Receiving Data from Terminal to FPGA using TTL

(I posted same question in stackoverflow but didn't get right answer) I'm newbie in VHDL. So today, after UART Tx, I tried to read Datas that coming from Realterm terminal. I only wrote Rx codes to ...
481 views

### Connect inputs of SN74LS08N to output of other TTL chips

I have a project in which I am making an 8-bit computer from TTL chips, I am using some SN74LS08N AND gates in the ALU. I know to set an input to HIGH, you must leave it unconnected, but for LOW, it ...
690 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 ...
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?
685 views

### True 5V CPLD other than PIC/Altera ATF150*?

Are there any True 5V CPLD's families still in manufacturing other than PIC/Atmel ATF150*? I am talking not just "5V tolerant IO", but rather ones with 5V VCCIO, able to drive 5V loads without ...
157 views

### 74AS TTL to CMOS pull up resistor and maximum speed (or lowest delay)

Hello I have to pilot a CMOS input 5V chip device with a 7474 flip flop with the lowest possible delay to minimize clock jitter. Signal is about 11.3 Mhz I have two options: 1) 74HC74 (CMOS ...
87 views

### 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 ...
65 views

### 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 ...
46 views

### 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 ...
131 views

### 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 ...
578 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 ...
246 views

### Difference between MAX3430 and ADM483 for TTL-RS485 Converter

I want to use TTL-RS485 Circuit as in the attachment. The circuit is working when I use ADM483 Transceiver for U1. It can provide communication. However the circuit is not working when I use MAX3430 ...
172 views

### HC-SR04 Distance Sensor Trigger Signal on 2.5V Voltage level gives no reading

I am using an Arduino on a breadboard setup with an ATMEGA328p MCU. The whole circuit is designed to work in a low-power state and is powered using a 3V (Nominal) voltage Coin Cell. The HC-SR04 is ...
193 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?
46 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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### 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 ...
150 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 ...
31 views

### 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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### 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 ...
94 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? ...
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 ...
62 views

### How to switch one output between two buses

I'm looking to take the output of some registers (e.g. 74LS670) and have them each be able to output either to an A bus or a B bus, obviously only one register can output on each bus at one time. I'...
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. (...
78 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 ...
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 ...
121 views

### 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, ...
50 views

### 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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### What is the True Pinout and Function of the 74ls181 in both of its modes (Active High and Active Low)?

I've found several datasheets for the 74ls181 with pinout and function diagrams as pictured below. This from Jameco (where I bought mine): https://www.jameco.com/Jameco/Products/ProdDS/46973.pdf ...
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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 ...
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 ...
20k 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 ...
74 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 ...
128 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 ...
796 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 ...
1k views

### 74181 ALU not working properly cascaded to add 8 bit numbers

I'm trying to make a homebrew CPU but having problems with the 74LS181 ALU, which I'm simulating in Logisim software before diving into real ICs and breadboards. I've cascaded two 74181 following ...
4k views

### USB to TTL communication problem

I'm trying to connect a device to my laptop using a TTL to USB converter like this one but it doesn't works so I tried the following configuration (USB to Serial, RS232 to TTL and then to the ...
75 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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### 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 ...
67 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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### 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 ...