Felipe Barriga Richards » diy

‘Cheap’ DMM (Digital Multi Meter) Hack (RS232)

fbarriga — Tue, 31 Aug 2010 03:05:11 +0000

After buying this DMM (VICHY VC99) (32.98 USD) I was curious to see what can be hacked so I open it. After removing all the parts I found below the LCD the IC that control this device: FS9922-DMM4. After searching for cool stuff in the datasheet I realize that it can output the LCD data trough a serial port. The datasheet contains an example of how to make this output serial port using an IR led to insulate the computer from the DMM.

Here is the schematic (Transistor: 2N3906; LED: IR204):

DMM Circuit Scheme

And here is some pictures inside the DMM to see where to attach the cables:

Power Connections	Data Cable
Data Cable in IC	Whole circuit

In another post I will put the information needed to make the IR receptor. For the moment you can see the final photos and the output data format. To use it in Linux I use the QtDMM.

DMM	DMM
DMM	DMM
Serial Port Data	Serial Port Settings

Clean Alkaline Battery leaks

fbarriga — Tue, 16 Mar 2010 16:55:04 +0000

Alkaline batteries can leak and start a corrosive process. When this occur it start to damage all metal parts of the circuits if you don’t stop it in time.

The corrosive agent is potassium hydroxide and an easy way to clean up this is using common vinegar. Only submerge it on a glass with vinegar and shake it every X minutes [I shake it when I remember that I've a glass with vinegar near my computer ].

Cleanning with Vinegar

Jetech LXM-500 UPS (Upgrade with Car Battery)

fbarriga — Tue, 16 Mar 2010 16:44:57 +0000

Upgrading Jetech LXM-500 UPS
After finding this old UPS I’ve decided to upgrade it with a 12V 55A car battery (the original battery was a 12V 5A).

Schematic of the comunication cable with PC
The communication cable used by this UPS is a straight pin-to-pin DB9 (Serial, RS232, etc).
The software is not available on Internet (trust me, I’ve been searching for hours before I found it in an old dusty box).

All files are the same (for search engine optimization only):

Replacing Original Battery with Car Battery
As the UPS can handle 500VA/250W at least I must take care of the ampere capacity of the cables.
The original cable was an 12 AWG cable which it can handle 25 ~ 30 Amp (source). As I like to take precautions I use an 10 AWG cable which can handle 30 ~ 40 Amp.

The easy part is to connect the 10 AWG cable with the battery using standard connectors. The hard part is to connect in a cheap and less complicated way both cables without soldering. For this purpose I’ve used two Feed Through Terminal per cable (they are rated 380V and 10A, so using two I can pass 20A).

LXM-500 UPS Circuit

Connector

Battery with Connectors

Removing the annoying beep sound
When this UPS is running from the battery supply it emit an annoying beep to alert the user. To ‘correct’ this you can simply remove the dammed buzzer.

Removed Buzzer

Safety
As you may know, if you short-circuit a car battery (lead-acid) it can generate Hydrogen and Oxygen gas. With a little spark you can have a big fire or even an explosion. To avoid this try to put the battery it a ventilated container, secure all connections and avoid the access of other people (children, stupid guys, etc). As a container I’ve used a toolbox with some baking soda at the bottom (the battery can leak acid so you can neutralize it with this).

As some finals words I don’t take any responsibility on this home-made super UPS and try to do things in the right way.