Questions tagged [ttl]

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

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59 views

Is voltage selector on 5v or 3.3v?

I bought this USB to TTL converter and it came with the option to switch between 5v and 3.3v. I want to use it at 3.3v, but I'm not sure where the (grounder?) should be placed? Thanks, see image below....
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55 views

Collector current in a BJT transistor whose base and emitter are forward biased

I'm reading a book about electronics and I have a doubt about a NAND gate implemented with Transistor-Transistor Logic. The question I have is actually about BJT transistors specifically (not the gate ...
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74 views

How do I switch a PIN diode using a TTL control signal?

I'm designing a transmit/receive switch for an antenna using a PIN diode. The PIN diode I'm using is UM7512 make: Microsemi. I need to switch between -400V (off) to +5V (on). The switching time should ...
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87 views

Is it common for such basic TTL gate chips as 74LS32, '08, and '86 to be broken? [closed]

I have too many failures with very basic gate chips, while the more complex chips seem to keep working fine. And I find that very puzzling. These aren't even CMOS where I know that a static discharge ...
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42 views

Automatic switching to the changed set of TTL inputs

I have 2 sets of 4 logical inputs. All inputs are active-low 5V TTL level lines with 4k7 pull-up resistors, as they may be pulled to ground by a a user pressing a switch or flipping a transistor with ...
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83 views

I need diodes to build a R-2R ladder DAC from original TTL chips (not Arduino) don't I?

I am thinking through how I could turn my analog oscilloscope with X-Y mode and Z input in the back into a simple computer monitor. I am learning about generating a proper sawtooth with a constant ...
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790 views

History question - why are logic levels inverted between TTL and RS232?

I'm just looking for a historical answer as to why TTL and RS232 don't transition logically in the same directions. The signals are the same, but basically level-shifted and inverted. Was there a ...
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43 views

Issues using a 74LS245 with Attiny85

I have a Raspberry Pi, a 74LS245, and an ATTiny85. I connected the Pi to the Tiny through 1k resistors, and am able to use SPI to program it, no problem. I have added a 74LS245 inbetween, to ...
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1answer
56 views

What kind of serial cable do I need? (TTL vs RS232)

So I have a headless NAS that I'm trying to connect to via a serial console so I can install a different OS. It has a 3.5mm jack on the back I/O labeled COM1. I had ...
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27 views

Chip shorting to ground when connecting the grounds

I have a pcb that converts USB to RS232, it is using a CH340G and a MAX2323. The output when not connected works as expected. I try to connect it to a separate device that has its own power supply. ...
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1answer
56 views

50 Ohm TTL Drive Strength

I'm designing a device that will output TTL (0-5V) over a 50 Ohm coax to an NI PXie-6672 with programmable 50 Ohm termination. I'm wondering if I will truly need 100mA of drive strength from my output ...
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Need to step down votage to test a heart rate monitor

I'd like to create a test bed for heart rate monitor devices. The type of monitors I'd like to test use chest straps to detect the voltage fluctuations caused by the heart. I'm told this votage ...
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1answer
106 views

TTL high input, outcome? [closed]

My books states that when a TTL input is high, the emitter diode cuts off and the emitter current is approximately zero. This animation shows that when a transistor input is high, the emitter diode ...
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4answers
831 views

Tachometer IC that does not require zero-crossings?

I recently built the basic tachometer circuit in this LM2917/LM2907 Datasheet shown below using the 8-Pin version of the device. I realize this circuit requires a VR pickup sensor, and so the LM2907/...
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1answer
33 views

Safety considerations (for parts) for a beginner building with expensive parts

I'm building for the first time (for me) a circuit with an expensive part (a $80 DEC J11 CPU) and would like to know some "safety" tips so I don't inadvertently destroy the thing while playing with it....
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100 views

Input and Output Impedance of a TTL NAND Gate

Basically I wanna know how to calculate the input and output impedance of this basic TTL NAND gate I have looked at several books and websites but found nothing useful , can anyone help me please. ...
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2answers
214 views

What are “Levels of Delay” in the 74LS138 data sheet?

I'm looking at the following three data sheets for 74LS138 devices: Texas Instruments SN74LS138, SN74LS138A Motorola 74LS138 Fairchild DM74LS138 Each has a "switching characteristics" table giving ...
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1answer
44 views

Help on translating 5V rotary signal output to interface with lathe's cnc controller!

I have a hall sensor (OH137 - open collector) as an index signal on my lathe’s spindle. I have the sensor pulled high by a 1k resistor and can’t change it because they’re both glued in epoxy. This ...
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66 views

Flashing program into microcontroller, usb-ttl, idea behind?

I have limited knowledge on this topic(MCUs, communication protocols, etc.). I back then worked with an STM32 MCU and did some UART(or USART, can't remember) communication between a PC and the MCU. ...
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1answer
46 views

Recommendations for On-Hand 74xx (and others?) ICs

I've been learning about logic gates (from Ben Eater's videos, etc.) and I find myself constantly having to order more ICs, especially 74xxs. Is there a list of ones I should keep on hand to help ...
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1answer
44 views

How to transition multiple down counters using 74ls193 in a 'one at a time' sequence

I've been messing with this circuit but i'm struggling to find the solution i'm looking for? Trying to create a sequence of down counter, so when the first completes the next starts and so on until ...
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1answer
54 views

How can I replace a SN74LS04?

I came across Ben Eater's Youtube channel and website and thought I'd give the clock circuit a shot (possibly doing the entire 8-bit computer thing in the future). He conveniently put list of items ...
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2answers
87 views

Working of a transistor in a TTL inverter circuit

I was referring to TTL inverter circuit in the book Digital fundamentals by Thomas Floyd and its working principles first proposition went as follows: When input is HIGH, Base emitter of Q1 is ...
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3answers
180 views

The circuit with 74HC138 is working, but with 74LS138 it is not, why?

I used 74HC138 in the first circuit and 74LS138 in the second circuit. Only the one with the 74HC138 is working. Why?
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68 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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31 views

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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182 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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2answers
82 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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2answers
39 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
165 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
79 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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265 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
743 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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60 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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120 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 ...
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1answer
52 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 ...
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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
199 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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57 views

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
71 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)\$ \$=(P+Q)S+(R+T)...
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126 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 ...
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1answer
108 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 pins,...
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34 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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1answer
457 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
118 views

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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132 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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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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68 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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65 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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