Curious timer design with disticnt VSS/VDD

Thread Starter

bxdobs

Joined May 11, 2014
27
Just received a selectable 0-99sec or 0-99min 12V relay board ... very basic and cheap so decided to purchase one instead of designing one myself ... very old school as this Chinese sourced product ground off the number on the only 14 pin soic on the board ... expecting it should be a MCU as it drives a 2 digit 7 segment display and uses a voltage divider (AIN) style IP to set the timer ... the curious part of their design is they used a 79L05 from the 12V rail to power this chip ... the second curious thing is this chip has VSS on pin 5 and VDD on pin 10 ... I have seen variations of VSS/VDD as 7-14, 1-14 but don't recall a 5-10 scenario ... as such, was expecting it to be simple to find the actual part they used. Ideas?
 

Papabravo

Joined Feb 24, 2006
18,409
Just received a selectable 0-99sec or 0-99min 12V relay board ... very basic and cheap so decided to purchase one instead of designing one myself ... very old school as this Chinese sourced product ground off the number on the only 14 pin soic on the board ... expecting it should be a MCU as it drives a 2 digit 7 segment display and uses a voltage divider (AIN) style IP to set the timer ... the curious part of their design is they used a 79L05 from the 12V rail to power this chip ... the second curious thing is this chip has VSS on pin 5 and VDD on pin 10 ... I have seen variations of VSS/VDD as 7-14, 1-14 but don't recall a 5-10 scenario ... as such, was expecting it to be simple to find the actual part they used. Ideas?
Putting VSS & VDD on middle pins is an old technique and probably means this is an in-house custom part. I think you have very limited options for figuring out what part they used. You could probably pick any MCU in a similar package and duplicate the functions with less time and effort than trying to figure out what the original manufacturer did.
 

Thread Starter

bxdobs

Joined May 11, 2014
27
Thanks ... my thoughts were that if they chose a custom package why go to the trouble of removing the label? TTL, 74LS etc are mostly discrete circuitry in that they wouldn't combine the functionality of Analog, Digital I/O all to affect a 2 digit 7 segment display and relay ... expecting the ic is either designed specifically for this app in some family of timer chips OR it is aMCU.

Does it matter ... not really. Yes, this design is simple enough to replace.

1 - dop f
2 - dop dp & dip Timer Start Sw
3 - dop d & dip Secs OR Mins
4 - dop d1 (left)
5 - Vss (Gnd)
6 - dop a
7 - dop b
8 - dop g
9 - dop e
10 - Vdd (+5V)
11 - dop Rly active low
12 - dop d2 (right)
13 - ain (0-5) V (0-99)
14 - dop c
 

Papabravo

Joined Feb 24, 2006
18,409
You misinterpreted. I did not say custom package, I said custom part. The package is a standard 14 pin package. The die inside is bonded out to the leadframe in the most convenient way. I do not think it is ANY kind of standard TTL, LSTTL or CMOS part. Once it is installed on the board there is no need to retain whatever markings it may once have had.
 

John P

Joined Oct 14, 2008
1,974
It could be a custom part, but not designed for the company that sells this product. Chinese manufacturers aren't always scrupulous about where their parts come from, and maybe this item is made for someone else, but the vendor who made it produced some extra components and sold them to competitors. If they did that, they might very well want to conceal the evidence.
 

Thread Starter

bxdobs

Joined May 11, 2014
27
Thanks all ... back in the day, if one was producing a large magnitude of product, there was the potential to order a Vendor-Specific IC with custom pinouts but that also came with custom markings ... I highly doubt there were enough of these boards made to warrant the added cost of changing the IC pinout ... John P's assessment sounds most plausible

After settling on a PIC 16C84 to do a project back in the early 90s, haven't spent too much time outside of the MC realm so thought someone here might have recognized this somewhat odd (not so common) VSS/VDD profile.

MC's RISC instruction set was easy to fall into having designed projects in the DataGen and 6502 worlds
 
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