H65 Infrared Thermometer from DealExtreme

DealExtreme is selling an infrared thermometer with measuring range of -20°C ~ 530°C. I bought that for generic use, but was positively surprised by the fact that it had a serial interface hidden inside.

There is a 6-pin male header at the battery compartment. It has 2.00 mm spacing instead of common 2.54 mm. I was using this type of connector to create a cable for testing.

There are clear markers on the PCB, if you take a closer look.

After some measuring, they seem quite logical, see table below. And if you google for MS6530 you will find a Mastech meter with quite identical specifications. With 4x the price. There are also models with A and B suffix having different temperature ranges. High-end models MS6550A and MS6550B are coming with USB data cable. Maybe with same protocol as this one ?

Number	Label	Description
1	G	Ground (Battery negative terminal)
2	V	Vcc (Battery positive terminal)
3	I
4	R	RX (Meter RS-232 receive pin)
5	_
6	T	TX (Meter RS-232 transmit pin)

This meter seems to have RS-232 Interface with 0/5V Voltage levels (Idle 5V). Looks like the configuration is 9600/8/N/1. Transmission is binary format and no specifications available AFAIK. However, I have made some observations.

When meter is powered off and trigger is pushed quickly, 2 measurements are performed. They are transmitted (and measured) with delay of 1.06 s.

Packets are usually 22 bytes long. Sometimes 16. They all start with bytes 0xFE 0xFE (Assuming LSB is sent first).

Some examples:

00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 21 22 

----------------------------------------------------------------- 

FE FE 31 34 0F 07 34 00 2D 0D A3 37 1B 00 09 01 08 01 FB 00 D1 F0  T:26.4C A:26.4C

FE FE 31 34 0F 07 39 00 30 0D B9 37 1F 00 0C 01 08 01 F9 00 43 F1  T:26.8C A:26.8C

FE FE 31 34 0F 07 39 00 36 0D AE 37 20 00 0D 01 09 01 FA 00 8D 0A  T:26.9C A:26.9C

FE FE 31 34 0F 07 3C 00 30 0D A6 37 22 00 0E 01 08 01 FB 00 EC 07  T:27.0C A:27.0C

FE FE 31 34 0F 07 3A 00 34 0D B0 37 21 00 0E 01 09 01 FA 00 D6 51  T:27.0C A:27.0C 

FE FE 31 34 0F 07 3B 00 37 0D AC 37 23 00 0F 01 0A 01 FB 00 65 15  T:27.1C A:27.1C 

FE FE 31 34 0F 07 3F 00 32 0D B2 37 25 00 11 01 09 01 FA 00 8D FE  T:27.3C A:27.3C

(continues) 

Hewlett packard 7015B X-Y Recorder retrofit

Not really a retrofit (yet), just wanted to try out EMC. HP recorder was closest thing to an XYZ table I could find in my storage. And the Z-axis is of course a pen holder solenoid.

X- and Y-axes can be easily controlled by feeding voltage to built in banana (lab) sockets, with simple DAC (This one obviously has integrated PID).

Plotter has an active area of about 260 mm x 195 mm. There are 3 different sensitivity levels: 5 mV/cm, 50 mV/cm and 500mV/cm.

This means I have following options for DAC range:

X-axis
5mV/cm * 26 cm = 130 mV
50mV/cm * 26 cm = 1.3V
500mV/cm * 26 cm = 13V

Y-axis
5mV/cm * 19,5 cm = 97.5 mV
50mV/cm * 19,5 cm = 975 mV
500mV/cm * 19,5 cm = 9.75 V

I have an old ISA-I/O card with 0...5V or 0...10V DAC ranges so I can easily get started. Card has 12-bit DAC's with enough speed. This means I can get resolution of 5V/2^12 = 1.2 mV/step. If I want to have full X-Y-range and use 5V reference, this leads to resolution of :

50mV/cm = 1.2 mV / x => x = 1.20 mV * cm / 50.mV = 0.24 mm

which is nice for testing. Even though I could just set reference voltage to 1.3V and get resolution of 260mm / 2^12 = 0.06 mm.

Let's see what kind of feed rated this resolution provides. If we move control servos using linear ramp and 1 kHz DAC, speed will be:

1000 steps/s * 0.24 mm / step = 240 mm/s. Is more than enough.
1000 steps/s * 0.06 mm / step = 60 mm/s. Still fast enough.

Z-axis does have only a switch, so some modifications are needed. Maybe relay or just an opto-isolator with FET. I just have to find control pins.

When pen is switched down, pins 3 and 6 in J2 are shorted. Pin 2 is also ground for PSU on-line indicator LED and pin 1 is anode.

(continues...)

DealExtreme cross hair laser

I have been looking for a decent cross line laser for my high speed PCB drill to come. DX had model (200)5982 which seems suitable:

Red Laser Module - Adjustable Crosshair (3.5V~4.5V 9mm 5mW) $2,97


According to my lab PSU it draws about 20 mA at 3.5V, 25 mA at 4V and 35 mA at 4.5V. Cross has good visibility in bright indoor lighting. They claim crosshair is adjustable, but there isn't any easy way to focus. This one has. Anyway, this is quite small laser in brass housing.