Need some help with BCD decoder. - Page 1
Forum section: electronics / beginners

author: WeekendHobbiest
author_rank: Newbie
timestamp: May 14, 2019, 01:52:59 am
content: Hello, everyone!BCDs seem simple in theory, but I am having difficulty getting them to work in practice. I'm not sure if I have a bad batch of ICs, or if I've overlooked something, or I am doing something wrong.I have a K511ID1 Nixie BCDs which I'm breadboarding. I am trying to get a LED to light using the truth table listed in the datasheet but the desired LED won't light. The only LED to light is the output 0, and that isn't by choice. The datasheet says that digit 0 is enabled when all inputs are set to LOW, so I am suspecting that my problem is the inputs.The setup I have done is supplying 5V and GND to the breadboard power rails using a bench power supply. I hooked up VCC and GND of the IC to the proper rails. I then jumpered the 5V and GND power rails to the A, B, C, D inputs for the digit (LED) I want to enable and the expected LED doesn't light.My troubleshooting attempts were:- Verified the voltage- Verified the wiring- Verified polarity of the LED to the IC (The LED has a current limiting resistor)- Swapped ICs (I have five chips).- Swapped breadboards- Wrote an Arduino sketch testing the the inputs (a simple blink program)- Verified that the datasheet I was using (TI's SN74141) was correct by looking at other related datasheetsThe chips are NOS with identical date codes. The likelihood of all five ICs being FUBAR out of the box seems slim (unless I did something unintentionally dumb).I can't figure what else I could overlook, so now I am stuck. Please advise. Thanks!

author: rstofer
author_rank: Super Contributor
timestamp: May 14, 2019, 02:02:29 am
content: As near as I can tell, the pinouts for the two chips are different. Which device are you actually trying to use?https://datasheet.octopart.com/NTE74141-NTE-Electronics-datasheet-32009451.pdfhttps://lib.voltradio.ru/k511id1.pdf

author: WeekendHobbiest
author_rank: Newbie
timestamp: May 14, 2019, 02:43:29 am
content: Hello, rstofer!The datasheets I've been referencing from are:https://www.alldatasheet.com/datasheet-pdf/pdf/115763/TI/SN74141.htmlhttps://tubehobby.com/datasheets/k155id1.pdfThese are what I pull up from and internet search for 'K511ID1 datasheet' (which is what the IC was sold under). The first pdf you linked matches the two datasheets I've used, but the Cyrillic script silk screened on the IC matches the second pdf. I assumed that 'K511ID1' was an Anglicization of Cyrillic script 'К511ИД1'!Going to try the pinouts on the second datasheet you linked to see if that works. I hope I didn't destroy these chips!edit: Which pins are VCC and GND on the second datasheet?

author: rstofer
author_rank: Super Contributor
timestamp: May 14, 2019, 02:51:16 am
content: Quote from: WeekendHobbiest on May 14, 2019, 02:43:29 amThat K155ID1 datasheet link actually points to a datasheet for the 74141.I have never used the Nixie driver so I know less than nothing about it but I think I would tend to consider the Russian link.Considering you don't know input from output, I would be using 220 Ohm resistors between the pins and Vcc or Gnd. In the final project I would never pull a pin to +5 without using a resistor. Pulling to Gnd is ok. The resistor can be on the order of 1k (usually).

author: floobydust
author_rank: Super Contributor
timestamp: May 14, 2019, 03:32:20 am
content: The 74141 has open-collector outputs, so your test LED's would go from +5V through a resistor to the 74141 output. They are active low.TTL inputs float high, so you must ground the BCD inputs low for a logic 0.edit: the power/gnd pins are in oddball location, something to check esp. if you get a false zero.K155ID1, 74141, 7441, datasheets:http://www.tube-tester.com/sites/nixie/74141-NDT/74141-NDT.htm