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i attempted make myself 2-in-1 programmer can program both at89cx051 , at89s52 on same board without having plugging/unplugging of port. the main issue strobe pin aka reset (rst in circuit). (pin 1 of db25 connector). tested pc , got no results. what seems work if connected rst vcc via 1k resistor. works because though output @ 3.8v instead of 5 (which vcc at), puts at89s52 in reset mode expected, i'm not getting 12v @ pin 1 of small at89cx051 socket. if don't make manual connection, 1.4v measured @ rst, after added 10k resistor between vcc , rst. without rst being forced ground, should 5v i'm not. i have tested transistors manually leg leg using diode setting on multimeter , turned out fine. resistors going base of transistors 2.2k , used 1k resistors in place of diodes. other resistors 10k. resistor going buffer (74hc125) 0 ohm. all capacitors 0.1uf. why getting such awkward voltages reset pin? using weak of resistors or something? update so ended ma...

i'm trying find "same or better" equivalent replacement 747 opamp. footprint / pinout can different, don't mind. using parametric search on arrow, while reading datasheet 747 found lt1355 might replacement. however, quite expensive; $16.89 1 single ic (dip package). searching lt1355 on octopart shows arrow cheapest one, price steep me. i'm fine around $8/pc. what other dual opamps can serve replacement 747? usually asking products/parts off-topic since can benefit wants better 741, i'm making exception. there literally hundreds of suitable 741 replacement opamps. the parts list waaaay expensive. have special properties few designs need. you should not looking 741 replacement per sé more "generic opamp". there usable opamps had less money. lm358, 10 1 euro (shipping included!) on ebay other examples: mcp602, ca3140, tlc271 most of these have versions 1, 2 or 4 opamps in 1 housing. you have compare datasheets see suits ...

below want select , edit bottom wire of 3 parallel wires: but when click on bottom wire program selects middle wire because share same net. is possible single out desired wire segment without selecting entire net in altium? yes you need use "break wire" feature first - split wire up. think it's in "edit" menu.

i have apc ups 9 ah battery. would ok replace 18 ah battery? i realize modifications needed since won't fit in case. in theory shouldn't matter how bigger ah rating of battery long regulate current , voltage same. takes long transfer coulombs of charge. bigger battery of same chemistry have larger capacitance , may have lower esr.

i'm trying make push-pull audio amplifier pair of power darlingtons (tip142 , tip147), i'm having problems biasing. here's diagram of 1 of configurations: here i'm using 3 diodes, used different things in place try correct biasing voltage. with biasing voltage lower 2.2 v (between bases of transistors) has crossover distortion, because there'll small parts of signal none conducting. with 2.2 v or more, both conducting , there's no more distortion, there's problem: current flowing between them escalates heat until take on fire (being starting current isn't great , they're on large heatsink, heatsink doesn't have time heat, fast happens). they're stable biasing voltages lower 2.1 v, there's distortion. the components heating here output transistors, i've cheked , none of resistors or diodes heating up. i've checked if negative feedback help, didn't, because voltage in output doesn't change current flowing t...

can sample , recover signals non infinite "length" using nyquist shannon theorem? example if have signal $$ x(t)= u(t+5)-u(t-5) $$ , know sampling period t less 10s (t<10). can recover using nyquist theorem? if not , recover it? edit: have taken fourier transform of signal , : $$x(ω)=2i(\frac{1}{iω}+πδ(ω))sin(5ω)$$ can lead finding period $$\frac{2π}{5} $$ , see if f>= 5/π can recovered. may not possible because used theorem although on finite signal no need think "finite length". though continuous time signals defined infinite time interval, in practice analyse in finite interval only. x(t) defined in interval [-5 5]. the frequency domain representation of such signal infinite bandwidth sinc function. hence not possible define particular sample rate per nyquist theorem, reconstruct without losing information. can sample definite sample rate, implicitly band limits signal. sampled signal after reconstruction through dac , lpf, not pe...

i have old audio amplifier (jvc a-gx2b) produces crackling noises on 1 of outputs. so, opened , discovered 2 largest capacitors seem leaking : can replace capacitor same characteristics (4700uf 50v), or should instead take specific capacitors audio? if yes, ones ? in addition, have interest replace capacitors of amp (not 2 largest)? 1: wear safety gloves when handling toxic leaky capacitors, remove , clean safely isoprop. , mark note polarity (-) 2 : measure dia , lead pitch dxl [mm] sort parts this 3: audio or better low esr, highest ripple current caps. < 50mohm, > 3aripple 4: better caps run cooler lower esr , rated higher temp. may not fit. 5: japanese caps have better reliability i suggest 1st choice panasonic @ digikey .. cost of shipping may more cost of caps. as suggested: cap voltage must same or more - capacitance tolerance doesn't matter, , may larger value. - large e-caps may replaced @ same time.