Can I substitute a 5V 1N4148 signal diode with a 5.1V IN4733A zener diode? - Page 1
Forum section: electronics / beginners

author: brinstar117
author_rank: Newbie
timestamp: December 21, 2020, 05:23:57 pm
content: Hello all,I'm trying to turn my Arduino into a rudimentary oscilloscope as outlined in the following link:https://www.electronicsforu.com/electronics-projects/pc-based-oscilloscope-using-arduinoThe circuit diagram and description call for 5V 1N4148 signal diodes for current limit protection and recommend them due to their fast switching nature. I don't think I have any 5V 1N4148 diodes but I have 5.1V IN4733A zener diodes. Will those work without issue? I have some other loose diodes but I'm having trouble identifying them. My loose components come from a used electronics kit I picked up from a garage sale.I want to use the Arduino oscilloscope to see if my computer motherboard EEPROM is receiving clock signals and/or outputting any signals.The motherboard, an ASUS PRIME B450M-A/CSM powers on but does not output video, does not POST, and does not issue any error beeps with a buzzer speaker placed on the speaker header.I do not know the history of this board as I purchased it as non-working hoping it was an easy fix based on the seller description. On other motherboards I have reflashed EEPROM chips to replace the corrupted data and have removed bad chips and soldered replacement EEPROMs to fix motherboards. However, this motherboard's EEPROM chip appears to be okay so I'm trying to diagnose the issue(s) keeping the motherboard from booting.The EEPROM is a Winbond W25Q128FWSQ and according to the spec sheet it requires between 1.65 to 1.95v supply. There is 1.87v running to it according to my freebie Harbor Freight digital multimeter. I would appreciate any suggestions on what I should try testing as I have not done this type of diagnosing before. My only experience is replacing some mounted components that were easily identifiable as broken like burst electrolytic capacitors.

author: David Hess
author_rank: Super Contributor
timestamp: December 21, 2020, 05:37:27 pm
content: Quote from: brinstar117 on December 21, 2020, 05:23:57 pmCounter intuitively, protection diodes on oscilloscope inputs are usually slow because they are optimized for low leakage. The long recovery time of a slow diode only means that the input will take longer to recover from an overload and faster recovery is not always required.So 1N4733A zener diodes are likely to work in place of 1N4148 switching diodes in your case but neither are really suited to the application. If you really want a fast 5 volt diode, then use the base-emitter junction of a 2N3904 transistor; these are faster than 1N4148 switching diodes and can recover in 100s of picoseconds while also being low leakage. A slower but higher voltage low leakage diode is the collector-base junction.

author: wraper
author_rank: Unknown
timestamp: December 21, 2020, 05:40:12 pm
content: 1N4148 has nothing to do with 5V you mentioned several times. It's a regular diode rated for 75V reverse voltage, it's not a Zener diode. If you want to use 5.1V Zener diode, then you can put it in place of D2 and not use D1 at all.

author: ocw
author_rank: Regular Contributor
timestamp: December 21, 2020, 05:50:43 pm
content: For the circuit which you reference, you need to use a switching diode like the 1N4148, not a zener. D1 limits the input voltage to a little over 5 volts while D2 protects against a reverse polarity input.1N4148 diodes are a common and inexpensive diode and are something handy to have available for future projects.

author: ozcar
author_rank: Frequent Contributor
timestamp: December 21, 2020, 07:06:27 pm
content: Quote from: ocw on December 21, 2020, 05:50:43 pmYes, always useful to have.I purchased 1300 1N4148 diodes for a particular project. The design was still in a state of flux, and in the end I had a few hundred left over. That was around 45 years ago (long live 1N4148!) and resulted in me having a lifetime supply. At the rate I use them, could be several lifetimes.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 21, 2020, 08:33:10 pm
content: In the given circuit a base-emitter junction of a small transistor would be an option. I somewhat doubt the BE junction would be really fast my guess would be some 100-500 ns, but no need for a fast diode here. For higher current capability base and collector should be used.The zener diode can work for a first try. Just keep in mind the leakage can be quite high well below 5 V and zener diodes usually have quite some capacitance. The Arduino's ADC is really slow - so one may still be OK.

author: george.b
author_rank: Frequent Contributor
timestamp: December 21, 2020, 09:16:26 pm
content: Quote from: brinstar117 on December 21, 2020, 05:23:57 pmThe rudimentary oscilloscope project you linked has a quoted sampling rate of 12kSa/s. The speed at which a modern BIOS chip communicates is much higher than that. You wouldn't get anything coherent out of that and it might confuse you further. You could just reflash it regardless, if you suspect it might be corrupted (dump it first to be on the safe side, that could tell you whether it's corrupted or not anyway).Have you checked all power rails on the motherboard? Zeroth rule of troubleshooting: thou shalt check voltages.