Questions tagged [ttl]

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

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4 answers
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Do stateful 74LS series chips start in a defined state?

Specifically, 74161 counters and 74377 registers, can I rely on them to be full of zeros on power on?
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1 vote
1 answer
112 views

What is this chip called? [closed]

I need a TTL chip 74 series, that takes in some amount of inputs and one enable bit. When the enable bit is high, the output is the same as the input. When the enable bit is low, the output is all low....
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1 vote
1 answer
52 views

K155ID1 power dissipation

I build my own nixie clock with four digits (IN-14, 10k anode-resistor) with a seperate K155ID1-IC for each digit (so no multiplexing). Also, I am only using the 0-9 range, so every tube has one digit ...
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0 votes
0 answers
27 views

ESP32-C3-WROOM: error flashing chip

I am developing an ESP32-C3-WROOM custom board, but when I tried to flash the chip using UART (FT232D USB-TTL) and Arduino IDE, I got the message "A fatal error occurred: Failed to connect to ...
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0 answers
93 views

Could I have a whole batch of bad AT26C16 EEPROM chips?

I am in TTL chip heaven (India) where I can get these things for pennies on the dollar, so I bought batches of chips to tinker with. Among them a 16 AT28C16 EEPROMs, looking like new, and then 2 very ...
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0 votes
2 answers
79 views

To drive current with open-collector gate when input is high, do I need a buffer or an inverter?

Once upon a time I knew the answer, or could just try it. But with distance I forgot. When I use an open collector, I do it to drive some load. So High means current is flowing. But when it is used as ...
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0 votes
1 answer
102 views

Frequency counter schematic

I was wondering what's wrong with my Proteus schematic. This schematic is supposed to show the frequency in Hertz on the display but instead only three zeroes are displayed. Is there any component ...
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1 vote
4 answers
182 views

74xxx logic. Cheapest, most space saving way to invert 10 logic outputs

Please see this circuit. I'm trying to design a circuit that allows you to use a single button to increment a counter from 0 to 9 (then it will loop). Diode logic will convert the 10 logic outputs to ...
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3 votes
2 answers
374 views

Is there a standard way of doing a TTL Hi-Z buffer?

I found many examples of IC internals for CMOS Hi-Z (tristate) buffers, but none for the TTL family. I guess that in the TTL world, the "open collector" is much more common, but I see that ...
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0 votes
1 answer
44 views

Schematic Review: PIN diode switch driver

I've designed a PIN diode RF switch driver, specifically to drive HP33000 series switches. Unfortunately, these are very old, and not much documentation exists, so I'd like to ask for advice from ...
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2 votes
1 answer
124 views

Correcting the lower output level of a square wave generator

I have assembled a square wave generator following this schematic from an old book. R1 and R2 are both 1 kohm, C1 is 68 pF, and C2 is 2.2 nF. The author of the book claims that this combination is ...
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3 votes
5 answers
665 views

Extending signal duration

I have DMM which is producing pulse with duration of around few microseconds. The pulse need to be sampled in PLC, which has sampling rate of 1ms. In other words the cycle loop can't be reduced to ...
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2 votes
1 answer
100 views

1 wire to 2 wire bidirectional UART

I'm working on diagnostics program for my old GM diesel, the old GM diagnostics uses a 1 wire bi directional serial protocol, 5v HIGH, 0v LOW, with the PCM data line being held high when idle, and the ...
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0 votes
1 answer
54 views

Connecting Arduino to Keithley external trigger

I need to connect digital output pin of Arduino Uno to Keithley DAQ6510 digital multimeter external trigger input. Both are utilizing 5V TTL logic. Now when I measure the voltage on external trigger ...
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1 vote
0 answers
78 views

Confusion In Fanout of Logic Circuit and Transistor

Fanout:-Maximum Gate we connect to output of any Logic gate. so there is limited number of gate we connect the output of Logic Gate.hence there is some minimum condition required for operation of ...
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1 vote
2 answers
90 views

How worried should I be about a short circuit lasting a couple nanoseconds? [duplicate]

Say I have two driver gates hooked up to each other in the following arrangement: In theory when A goes low, for a brief amount of time B will be shorted while the 7404 inverter gate switches. Around ...
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0 votes
0 answers
66 views

FT232RL Chip is not working (USB to TTL)

I used an FT232RL chip to make a USB to TTL converter using the schematic below. Although I can send a message and the TX LED is lightining up, I cannot receive any messages. Can anyone see a problem ...
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0 answers
49 views

How to correctly terminate a TTL line between two ICs?

I am designing a circuit to convert a 5ns ECL signal to an LVTTL signal of >10ns. The SY100ELT25 is used to convert the ECL to 5V TTL which is then fed into the SN74LVC1G123 to further reduce the ...
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0 votes
2 answers
99 views

Peak/envelope detector circuit for 30 MHz sine pulses with a 10 kHz PRF

My goal is to input 30MHz sine pulses, with a pulse width of 10us and gap of 90us between the pulses. The circuit should convert this pulse train to a TTL signal that goes from 0 to 5 volts. To ...
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1 vote
2 answers
119 views

MAX3232: Switch between RS-232 and TTL levels

Sorry in advance, electronics noob here! I need to make a proof of concept to get some data out of third party system which handles both RS232 and TTL levels. The computer/raspberry/arduino shall - I ...
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2 votes
1 answer
131 views

74HC74D initial output value after power up

I use a touch sensor (Active Low) to light up a light bulb. here I've used a 74HC74D D flip flop to turn on an off the bulb with the sensor pulse (sensor output is active low which is then converted ...
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1 vote
1 answer
48 views

Can I repair CY62256 with UT62256

The CY62256-55PC(SRAM) in my old computer is broken and I need a replacement for it but I can't find the same chip. The only one similar enough in my local store is UT62256CPC-70LL, HM62256ALP-12 and ...
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0 votes
1 answer
207 views

Changing voltage level from an incremental encoder from 5V to 3.3V for my Raspberry PI Pico ADC pin

Edited I want to read data from my DC machine through a Sendix 5000 (encoder datasheet) incremental encoder with a Rasberry Pi Pico. Optical encoder with RS422 output and 5VDC supply. The HIGH ...
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3 votes
6 answers
1k views

Reduce 3.3 V-8.4 V signal to 3.3 V input

I have a digital input signal which can use anywhere between 3.3 V and 8.4 V to signal "1", and I need to make this safe for a 3.3 V input on a microcontroller (RP2040). I currently have a ...
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1 vote
0 answers
75 views

What is the shortest pulse a controller can count?

I want to count short LVTTL pulses (about 20-25 nanosecond.) Right now, I use an Arduino with four IN74AC161N binary counters, but this solution has some Arduino limitations. I count pulses, send the ...
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0 votes
0 answers
120 views

Equivalent of multiple emitter transistor using regular one emitter NPN BJT transistor

I want make a simple NAND gate using transistors with transistor-transistor-logic aka (TTL). I saw on tge Internet (Wikipedia) that it requires two emitters as inputs. Source: https://id.m.wikipedia....
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7 votes
3 answers
462 views

Tying open-collector outputs to TTL inputs

I know that open collector outputs are effectively either 0 V or high-Z. I also know that TTL chips tend to read a disconnected output as high, but that really you should have something like a 1 kΩ ...
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4 votes
3 answers
1k views

Why does the TTL NAND gate use a 4 transistor design instead of 2?

Why does the TTL NAND gate use 4 BJTs to make the gate when it could be done using only 2? I assume that the design with the 4 transistors amplifies the current so multiple levels of gates can be ...
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0 votes
0 answers
173 views

Fan-Out Calculation on LTSpice

I need to find the fan-out of the circuit below. This is a Schmitt Trigger TTL NAND Gate. How can I exactly find the fan-out of the given circuit using LTSpice or calculate it theoretically?
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1 vote
1 answer
110 views

I'm designing a 4-bit GPU and I need some suggestion about the RAM for it [closed]

I'm working a 4-bit GPU, the GPU run on 1.023MHz (1023kHz) clock while CPU only run on 127kHz so I need a screen buffer for it when the CPU is working on some instruction. The display I use is a 24 x ...
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0 votes
3 answers
142 views

TTL voltage drop

I recently bought a lot of TTL components like 8-bit registers, bus transceivers, etc. to build an ALU and 2 registers. My issue is that when I build a register, the voltage drops to 4.2, sometimes ...
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0 votes
1 answer
58 views

How can I find reverse current of 74lsXX integrated circuit

I'm using 74lsXX ICs for my 4-bit computer. I noticed that 74XX ICs have reverse current at the input; I know that the output of the IC allow the reverse input current flow back to it. But I'm a bit ...
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1 vote
1 answer
136 views

Can MAX485 TTL-to-RS-485 module be used as UART-to-RS485 module?

I'm trying to make a bridge from Modbus til Home Assistant using an ESP8266 (as outlined here), which uses an UART-to-RS485 module. I have this MAX485 TTL to RS-485 Interface Module. I'm not competent ...
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2 votes
1 answer
267 views

I have a JK flip-flop circuit that works in simulation, but not with real components on a solderless breadboard

I'm building a control mechanism for a seat heater in my car. Eventually, it will drive power relays to control the current to the heating elements. It works in a simulation on simulator.io, but it ...
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0 votes
3 answers
404 views

How do you make a three input NOR Gate function as two input NOR Gate?

Hi this is my first question! So I'm clearly a beginner in electronics and studied for months, now the topic I've studying is logic gates and boolean algebra also the TTL ic. I've been curious if how ...
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2 votes
2 answers
587 views

Logic level converter from 29V to 5V schematic

Does it looks a good schematic to do a proper 29 V to 5 V logic level conversion, any improvements or suggestions?
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0 votes
3 answers
150 views

Connecting a GPS to computer: Jackson Lab LC_XO serial TTL to RS232 port on computer motherboard

I am trying to hook up my Jackson Labs' LC_XO GPS disciplined oscillator (GPSDO) to my computer motherboard COM/serial port so I can talk to it and for it to send back NMEA messages. Basically, I am ...
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0 votes
1 answer
97 views

How to connect RS232 level shifter?

I'm trying to use this: https://www.sparkfun.com/products/449 to connect my RPi to my computer via a USB to serial device. (And eventually connect the RPi to other legacy serial devices) My questions: ...
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0 votes
2 answers
594 views

SIM800L V2 not responding to AT Commands from Putty over USB-To-TTL PL2303

My SIM800L V2 RoHS (the blue one) although it connects to the network and registers just fine, it's not responding to AT commands sent over the PL2303 (USB-STC-ISP) USB-To-TTL Adapter through which it'...
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2 votes
1 answer
92 views

Is there a problem with a resistor inline between two TTL gates?

I want to adapt the output of a board to drive additional logic instead of an LED. The driver board has a current limiting resistor before the signal is routed to the connector. Is there any problem ...
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5 votes
3 answers
923 views

Why am I seeing -5 V or lower on the output pins reading an Intel 1702A EPROM?

I am building a breadboard/Arduino reader to dump the data on a very old Intel 1702A EPROM chip. (data sheet) When doing some basic testing by tying all the address pins to ground, I am seeing ...
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1 vote
1 answer
102 views

Trigger TTL input signal with a micro switch

I used to have a machine where an action could be triggered on a pontential free contact with a simple micro switch (that worked pretty easy and well for me). That machine got replaced and the new ...
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2 votes
2 answers
692 views

Convert PWM to TTL signal via IC or circuit

I'm fairly new to TTL logic. I have a PWM output 0-3.3V that I need to convert to a TTL 5V logic as the sensor only accepts a TTL signal. Is there an IC that would do this or a circuit I can build?
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0 votes
1 answer
153 views

SN75176 with 3.3V

Can I connect the SN75176 RS485 transceiver with a 3.3V microcontroller? The datasheet says that it must be powered with 5V and all inputs / outputs are TTL, but I'm not sure since the minimum high ...
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1 vote
1 answer
127 views

Why does the 74LS32N behave like an AND gate?

First of all I am a beginner. I am practicing with the 74LS32N (OR Gate) IC , I noticed that it behaves like an AND gate instead of an OR Gate. Only when both the inputs are 1 , the output is 1 , (Led ...
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0 votes
1 answer
101 views

8-channel/octal equivalent of 74HC125

I have a 12v powered 16-channel relay board, that required 5v logic level signals to control the relays. However, I am using a Raspberry Pi to control this, which has 3.3v logic level outputs. I have ...
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0 votes
1 answer
115 views

74HC08N doesn't latch [closed]

I am using the 74HC08N chip. Why doesn't the first AND gate latch itself? I have connected the output of the first AND gate to its own input. I have used two resistors, the one on top is a pull-up and ...
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0 votes
0 answers
44 views

What is "level of saturation" for transistors?

This is a term I've never heard of, and it's presented on a work analysis of a ttl nor circuit. It basically says that the transistor that links the output with the ground should have a higher "...
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  • 101
1 vote
2 answers
114 views

What is the function of the latch pin on my 74HC595 IC?

I am using this code with a 74HC595 IC to control a 4 digit 7-segment: ...
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1 vote
2 answers
676 views

How do I step down a 12V pulse width modulation signal to 5V?

I want to control my new laser module from my repurposed 3D printer. The laser module has a 12V pin for power, a ground pin and a 5V PWM pin. My board's fan-control port can generate a 12V PWM signal, ...
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