Tagged Questions

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

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2
votes
0answers
113 views

Need help with a sub-standard RS232

I've built a UART-RS232 converter based on max232 and it works well... but not for what I need :) According to Maxim's datasheet the RS232 side signal voltage should be theoretically +/-10v (5v * 2), ...
0
votes
3answers
69 views

Add a Tunable delay to a TTL pulse?

How can you add a tunable delay to a TTL pulse? My understanding is that this is the job of a PPL. I am not sure if a digital PLL delays a square wave or if it can also delay a single rising edge ...
1
vote
1answer
77 views

How could I efficiently implement this “TTL load”?

I'm attempting to test a parameter of an IC to the specifications listed in the data sheet. The data sheet describes the following load circuitry for the output: The data sheet notes that CL be ...
3
votes
3answers
158 views

7805 5v Regulator outputting 5.8v? TTL chip not functioning correctly? LED + TTL chips?

I've read a number of other similar questions to mine, but none of the answers have helped me so far. I also don't have any electrical schematic software, so I'm afraid I'll have to explain in words ...
5
votes
2answers
83 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 ...
1
vote
3answers
181 views

Will a 3V3 rated UART be damaged by applying 5V signals?

If I have a device specified for 3.3V operation and I connect a 5V level TTL signal to it ? Will it's UART ports be damaged or not ? I have a WiFi module and I want to know if its UART ports will ...
3
votes
2answers
89 views

Digital Clock --->Bad Accuracy (Help to Troubleshooting)

INTRODUCTION: I'm a student in the Electronic Engineering program at my University. I'm building a digital clock as a self initiative to learn more. Some of the requirements and steps that is ...
5
votes
3answers
218 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
481 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 - ...
2
votes
3answers
143 views

Drive Fight on 7400 Series

I'm currently designing a 7400 series circuit to drive LEDs from a set of shift registers (74595). Each shift register's tri-state input is wired to the output of a 2:4 decoder (74139), and the ...
0
votes
1answer
156 views

How to get a CVBS signal into an TFT LCD Panel over TTL

I have a TFT LCD panel from Chi Mei, namely G104V1-T01 on which I want to show a PAL composite video signal. As the datasheet tells me, this panel uses TTL (as opposed to LVDS) for data transfer, so I ...
2
votes
2answers
124 views

Synthesize VHDL into discrete TTL integrated circuits

I've got a small project in VHDL (fully working in a Xilinx FPGA) and I would like to implement it using an old-school printed circuit board and discrete TTL integrated circuits, in the spirit of ...
0
votes
2answers
116 views

Gating TTL UART Tx pin to simulate BREAK for arbitrary time periods

I need to gate a TTL Tx pin @115000bps as the chipset that drives the RxTx lines do not implement UART BREAK for arbitrary time periods. Thanks to this community's feedback (Selecting proper vales of ...
1
vote
2answers
410 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 ...
4
votes
2answers
238 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. ...
2
votes
2answers
207 views

Clock Pulse from Audio Signal (Laptop Headphone Jack)

Been fiddling with some circuits on breadboard to get a stable clock pulse from an audio signal via a laptops headphone jack. Reason 1: Other precision sig gennies are out of the budget right now ...
0
votes
1answer
2k views

Arduino as modbus master with MAX485 doesn't get any response

I'm having some troubles trying to query a modbus slave with an Arduino through RS485. I've already succeeded in querying a software modbus slave running on my PC through the USB/COM port using the ...
4
votes
1answer
368 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 ...
3
votes
1answer
1k 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 ...
1
vote
1answer
108 views

Whats the most interesting to build with 7400 series [closed]

I'm currently doing a project and have no idea what to build
2
votes
0answers
166 views

Decoding 125kHz ASK signal [closed]

I'm looking to decode what seems to be a 125kHz ASK amplitude shift keyed signal (1 V p-p). I'm saying ASK, but it may not be the right term. It's basically a 125 kHz signal or a 1V constant voltage. ...
3
votes
3answers
60 views

Does this buffer's current rating apply to each individual output, or all of them?

I'm thinking of using a SN74ABT244A octal buffer in a circuit that requires the buffer to sink 20mA of current on all eight outputs under worst-case input conditions. In the datasheet, it says that ...
2
votes
1answer
341 views

how to interface HCPL-3700 optocoupler to an input pin of ATmega16L

I want to detect logic of the mains supply (230VAC, 50Hz) and feed the output of HCPL-3700 into ATmega16L. I read through the datasheet but could not understand how to calculate the resistor values. ...
0
votes
1answer
593 views

How to connect RN-131 (wifi module) to RN-SRL-PRO3V-DGL (USB-to-TTLdongle)

I guess you might think that this question has been asked before, but what I need to ask is something very different. I have RN-131 which is a wifi module from Roving Networks and also ...
0
votes
2answers
326 views

Connection to a USB to TTL dongle

I have a USB dongle which converts TTL UART signal from a microcontroller to USB level signal using level converter. I has six pins Vcc, GND, RTS, CTS, TXD, RXD. My microcontroller has two pins for ...
2
votes
3answers
278 views

Which 74xx logic families are overvoltage tolerant on their outputs?

Here's my dilemma: I have a 3.3v active-low logic line, and I want to use it to drive a 5v active-low logic line. The 5v line already has a pullup, so my plan was to use an open-collector buffer IC ...
4
votes
2answers
1k views

Interfacing Arduino to C64's tape port

I'm working on a project where i'm using my Arduino to stream TAP tape data files from my PC to the C64. The software side of the project is going well however i'm still new to electronics and i don't ...
1
vote
3answers
243 views

Is it possible to build a inverter that operates at a frequency set by an LC tank using ONLY that LC tank and transistors?

I was always dissatisfied with inverters because it seems like an LC tank and transistors would be all you need. However, after much time spent simulating and a few false positives experimenting, I am ...
4
votes
1answer
354 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 ...
2
votes
2answers
4k views

Using Arduino UNO as a USB to TTL converter for unbricking a Seagate Barracuda 7200.11 Hard Drive

Is it possible to use an Arduino UNO as a USB to TTL converter for unbricking a Seagate Barracuda 7200.11 Hard Drive And if it is possible : how to program it? The Arduino UNO has no FTDI chip. In ...
2
votes
1answer
578 views

What is the fastest 7400 series family? Is 74VHC faster than 74AHC?

What is the fastest 7400 series logic family? Is 74VHC* faster than 74AHC*? This list does not seem to be in any particular order: http://en.wikipedia.org/wiki/7400_series
3
votes
2answers
190 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 ...
13
votes
8answers
1k 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 ...
11
votes
6answers
649 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 ...
1
vote
2answers
528 views

Boost Converter for TTL circuits to drive large loads

I've got a small PIC-based TTL circuit device, powered by a 4.5V coin cell, that needs to drive a solenoid which requires 12V. Obviously my logic level device can't directly power that so I could ...
1
vote
1answer
803 views

Creating a one-digit scoreboard using logic circuits

I'm creating a one-digit scoreboard on a breadboard. Naturally, I have a BCD to 7-segment decoder and a 7-segment display. But I don't know how to automatically increment the display. (It's for a ...
6
votes
1answer
822 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 ...
2
votes
3answers
554 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: ...
1
vote
2answers
765 views

PCB and trace design for high-speed TTL

I am designing high-speed TTL-based processor. I will be using only fast AC, ACT and LVC series, so switching frequencies will be in 100Mhz range with 1-3ns fronts. I plan to use homemade 2-sided ...
3
votes
3answers
2k 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 ...
5
votes
1answer
892 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 ...
2
votes
2answers
536 views

Is my SparkFun RS232 Shifter SMD faulty?

Product Link I am connecting this to an Arduino. (once Arduino programmed I removed the USB connector as it shares the serial comms with Pin0&1) RS232<->Arduino VCC <-> 5V GND <-> GND ...
4
votes
3answers
478 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 ...
0
votes
2answers
163 views

Three-state inverting octal buffer

I'm looking for a three-state inverting octal buffer for a replacement part for an old microprocessor lab. The package should be DIP. Ucc should be on pin 20. Chip select should be at pins 1 and 19 ...
8
votes
2answers
286 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 ...
7
votes
2answers
3k 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 ...
2
votes
2answers
544 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 ...
4
votes
4answers
2k 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 ...