missing op-amp chip in kill-a-watt?

[mrtz]

To my surprise, when I opened my kill-a-watt (P4400), it looks like a different design from what is described in the tweet-a-watt guide. It does not seem to have any DIP chip on the PCBs. Did they stop using an op-amp in their design? Anybody else seen this. I bought my kill-a-watt on amazon.com about 1 month ago. I've attached a photo of this. On looking closer, I see that the transistors used are: CJ 78L05 near the large 100uF capacitor and the other 3 are all ST 2N3904.

I ordered a tweet-a-watt kit from adafruit and hooked up everything from as per the online guide, but I'm not sure how to proceed now at the final hookup step. Any ideas? Thanks.

[adafruit]

can you post a photo?

[mrtz]

attaching the photo

[The_Don125]

Looks like the Kill-A-Watt got an update. Reading the product numbers on the main board, the one pictured in the Kill-A-Watt build guide has a product number of 65120001 revision C, while yours is P/N 65120002 revision A.

[adafruit]

please take photos of the other sides of the PCBs as well! i need to see what SMT chips are on there

[mrtz]

I'll take some more photos and post them later this evening

[chickensandwich]

The op-amp is on the other side of the pcb, located directly behind the lcd.

[mrtz]

The markings on on the smaller SMT chip was covered with a black marker or something. I scraped the top gently with a penknife and tried my best to zoom into it - some characters are not visible, but hopefully someone can identify the chip. The larger chip is "2902 JRC A8058B".

[adafruit]

fancy! yeah, just solder the ribbon cable to the SOIC op amp chip's pins. the pinout is the same. the indented dot is pin #1
it should work the same way, i doubt they changed the functionality

[mrtz]

fancy! yeah, just solder the ribbon cable to the SOIC op amp chip's pins. the pinout is the same. the indented dot is pin #1
it should work the same way, i doubt they changed the functionality

Are you saying that the A8058B chip in the new design is the equivalent op-amp of the LM2902N in the old design (described in the tweet-a-watt instructions)?

[adafruit]

A8058B is the date code

[mrtz]

I was confused. Thanks for your help - I'll try it out.

[mrtz]

Just as an update: I was able to solder up the surface mounted op-amp as per older instructions - ie same pin configurations as ladyada mentioned. Of course it was as little harder due to the smaller pins. But eventually, I think I got it right. To get the wires out from the LCD side, I made two little notches on the upper left and upper right of the PCB from which I let the soldered wires out to the other side. I made the notches to be careful, since I found it hard to get the wires out to the other side since the PCB is flush with the plastic case, and I felt that the wires may break internally or pull the delicate soldering off the op-amp.

Also, I have been able to successfully run the wattcher script too and I get power data as expected, so all is fine. I can confirm that the new surface mounted type op-amp in the new Kill-a-watt design is still usable with the standard Tweet-a-watt design and guidelines. I'll post some more photos of the hookup later.

[adafruit]

awesome! thanks for offering to take a photo. do you mind if i add this to the tweet-a-watt docs? i have 5 kaw's and all of them are the same style

[mrtz]

Sure, please go ahead. I'll post more pictures by the weekend to go with my description.