Is there a replacement for 74LS145, but with input latch? - Page 1
Forum section: electronics / beginners

author: LinuxHata
author_rank: Frequent Contributor
timestamp: June 19, 2022, 04:11:18 pm
content: Hello.For a certain project I need a chip, that is functional replacement of 74LS145 (BCD to Decimal decoder), but with input latch, so several of them can be used on same bus. I don't care whenever it is CMOS or TTL, or it's loading capabilities, since it will be driving some transistors anyway.Any ideas?

author: LinuxHata
author_rank: Frequent Contributor
timestamp: June 19, 2022, 04:39:47 pm
content: I actually already done it via MCU, just was curious, whenever there was such hardware product available, because there is say CD4543, which has all the features needed, but it is for 7 segment displays, not for 10 outputs. Also there are some I2C bus expanders, but they have 8 or 16 bit outputs, not 10....

author: Kleinstein
author_rank: Super Contributor
timestamp: June 19, 2022, 05:19:58 pm
content: There is the option to use shift registers as a kind of SPI port expander that can be scaled also for a large number of outputs. If needed there are chips (e.g. tpic6c595 and silimar) with integrated driver to directly drive slighly larger loads.

author: wizard69
author_rank: Super Contributor
timestamp: June 19, 2022, 07:33:03 pm
content: Is the one of ten upturn what you are looking for? If so nothing is coming to mind right now and my internet connection is so slow searching is a pain. There are so many variants on the market you would think somebody has had this need before and some body solved it..If you have a serial port available I'd suggest looking for a suitable serial device. Again may variants available and they are generally of newer design thus incorporating far more of the support electronics. Unfortunately devices that take BCD are not coming to mind at the moment. There are however plenty of BDC to seven segment drivers.You mentioned needing to use several on the same bus, that starts to be a lot of discrete I/O points. Is this the type of thing that can be refactored to port expanders or the IC sets targeted at industrial I/O? Just trying to understand why BCD to Decimal with the need for multiple outpus.

author: LinuxHata
author_rank: Frequent Contributor
timestamp: June 19, 2022, 07:35:29 pm
content: Yes I'm looking for 4 to 10 option and nothing comes on except 74141/74142, which were used with nixies and are not exactly kind I'm looking for.I do have some CD4514/4515, but these are large (physically), are 4 to 16 and smaller versions are 4 to 8, not 4 to 10.

author: Benta
author_rank: Super Contributor
timestamp: June 19, 2022, 07:46:07 pm
content: Quote from: LinuxHata on June 19, 2022, 07:35:29 pmOf course they are. 4-to-10 decoding plus power is 16 pins. Now you also want latch/clock signals etc? Minimum 20 pins, and this is unpopular at the manufacturers.Do you really need BCD-to-decimal in HW?I'd just do the conversion to decimal in the MCU and then clock out the whole shebang to a chain of 74HC595 parts.

author: ebastler
author_rank: Super Contributor
timestamp: June 19, 2022, 08:28:11 pm
content: It's another one of those discussions where the OP tells us what specific part they believe they are looking for, rather than telling us what they want to achieve. That tends to lead to sub-optimal advice and outcomes.

author: LinuxHata
author_rank: Frequent Contributor
timestamp: June 19, 2022, 09:14:30 pm
content: I know what I want to achieve and I know at least 9 ways of doing itHere I'm asking a super simple thing, without going deep into detailsFor the "BIG" size of CD4515, I meant it is in DIP case, no SSOP or similar small ones available.

author: ebastler
author_rank: Super Contributor
timestamp: June 19, 2022, 09:23:36 pm
content: And you have received your reply -- the very specific thing you very specifically asked for is not available. Go figure. Maybe use one of the other eight ways?I am a bit confused by the size constraint, by the way. If you have ten transistors and passives after each of the decoders, all of these presumably through-hole components since you seem to want to avoid SMD -- is the size difference between a 4:10 and a 4:16 decoder really the bottleneck?