福禄克8050A液晶显示器用LED取代讲课教案.doc

Fluke 8050A LCD display replaced with LED seven-segment
Recently I was able to cheaply buy a second hand Fluke 8050A made in the early eighties. It is a nice 4.5 desktop digit meter, but a typical problem seems to be that the LCD wears out and goes black. Replacement LCD displays are hard to find, not cheap and probably lead to similar problems in due time.
The LCD display is interfaced by standard components (CD4054 and CD4056) that drive each segment individually. This allows it to be replaced with a LED 7-segment display. However LCD displays are driven normal/inverted about 30 times/second. LED displays can be used by disabling this clock and connect it to a fixed level (high).
Since my Fluke does not have the battery option I was pretty confident that the power supply would be able to provide the additional LED current. The LCD drivers are able to sink current per segment in the order of 2mA. Sinking capability is somewhat higher than sourcing, so I decided on an LED display with common anode.
Since I had no idea how bright a LED display is with this amount of current, I ordered the brightest 9mm displays I could find. If they turned out too bright I could always reduce the current. And that is what happened. In the end a series resistor of 2k2 showed proper results. With 1k the display was brighter, but some bleeding to neighbouring segments started to become noticable.
The LCD display also has a couple of special symbols for high-voltage(HV), low battery(BT), decibel (dB) and relative measurement (REL). Of course these have to be handled differently and I simply printed them as inverted text on paper. The paper is then lit from behind with separate high bright LEDs. I blackened the laserprinter output a bit more with a felt pen.
Another special case is the plus (+) and minus (-) of the LCD display. Personally I do not see the need for a plus symbol, so I decided to use the minus only since the LED can provide this nicely. The most significant digit segment g is used for this purpose. To “disconnect” it from the digit I tipped a small peace of the segment with a black CD felt pen.
However the behaviour of the +/- signals is a bit strange. I have no knowledge of how this worked originally on the Fluke. After playing around what seemed to work in all measuring modes (R/V/A/dB and REL combinations) is to use the inverted '-' signal and disable the segment when '+' is high (??!!). Without using the '+' signal, measuring ohms has the minus sign always on. Oh, well, this can all be done using a single small BS170 mosfet.
Below is shown the detailed images of the whole process, the circuit diagram of the display board and the circuit modifications.
The new LED displays in stages
福禄克8050A液晶显示器用LED取代七段
最近，我能买便宜的二手福禄克公司在八十年代初提出8050A。这是一个不错的数字4.5米的桌面，而是一个典型的问题似乎是，液晶耗损，变黑。替换液晶显示器很难找到，不便宜，可能导致类似的问题在适当的时间。
接口的液晶显示器是由标准组件（CD4054和CD4056）的驱动每个单独部分。这使得它能够与一个LED七段显示器所取代。但液晶显示器的驱动正常/倒约30次/秒。 LED显示屏可以使用禁用此时钟，并连接到一个固定的水平（高）。
由于我的福禄克电池没有选择，我非常有信心认为，电力供应将能够提供更多的LED电流。液晶显示驱动程序可吸收电流在每段为2mA秩序。下沉能力略低于采购高，所以我决定在与普通阳极LED显示屏。
因为我不知道如何明亮的LED显示与此的电流值，我下令亮9mm的显示我能找到。如果他们原来太亮，我总能减少电流。这是发生了什么。最后一个包含2K2并且不同串联电阻显示正确的结果。随着1K的显示器是光明的，但有些出血到邻近的段开始变得明显。
该液晶显示屏还具有特殊符号的高电压（HV），低电池（BT）的，分贝（dB）和相对测量（REL的）夫妇。当然这些都必须处理不同，我只是印在纸上的文字为他们倒。该文件，然后从背后有独立的高亮度发光二极管点亮。余变黑的laserprinter输出多一点与毡笔。
另一个特殊情况是加号（）和减号（ - ）的液晶显示器。我个人认为没有必要为一个加号，所以我决定使用减去只是因为LED可以提供这很好。最重要的数字段克用于此目的。以“断开”，从数字我放倒了用黑色CD段小和平感觉笔。
但是在/行为 - 信号是有点怪。我没有怎么运作的有关Fluke最初的知识。围绕什么之后似乎在所有测量模式（读/电压/电流/ dB和REL的组合）是使用倒打' - '信号，并停用段时'高(??!!).如果不使用''信号，测量欧姆有减号始终。哦，好，这都可以使用一个单一小BS170的MOSFET。
下面是显示的全过程，在显示屏和电路板线路图修改了详细的图像。

在新阶段的LED显示屏

The bad LCD display

Replaced it with 9mm LED displays and 3 LEDs

With printed symbols on paper

Paper is made more black with felt pen
The selected LED display details:
Kingbright SA36-11SRWA
Red 9mm display
Common anode
Brightness 2200-9000 uCd @ 10mA
Conrad order code: 158780Dimensions:

9毫米显示红色共阳极
The Fluke 8050A display board circuit (photo)福禄克8050A显示板电路（附图）
Circuit modifications: 电路修改：

Note that each individual segment has a 2k2 resistor between it and the driver pins. I soldered the cut resistors directly to each driver IC and wired them from there to each segment. This was a bit more work then I expected... The symbol LEDs have 1k in series. For a Fluke with the battery option you would need an additional LED.
请注意，每个部分都有它与驱动引脚包含2K2并且不同电阻。我焊接电阻直接切到每个驱动器IC和有线从那里他们每个部分。这是一个多一点的工作，然后我想象... LED具有符号串联1K的。对于使用电池的选择福禄克那么你需要一个额外的LED。
The results:

Further ideas RS-232 interace:
Now I understand the circuit en have seen the signals on an oscilloscope, I was thinking of making an isolated RS-232 interface to this meter. It is a desktop model that is mains powered, so keeping it switched is not a problem. This would allow long duration measurements like rechargable battery charge/discharge curves etcetera. To isolate the circuit to be measured from the computer would also require an opto isolated interface. It might never happen, but if it does I will update this page.
进一步设想的RS - 232 interace：
现在我明白了电路连接在示波器上看到的信号，我是做一个隔离的RS - 232接口，此米的想法。这是一个桌面模式，即电源供电，因此保持它切换是没有问题的。这将允许像充电电池充电/放电时间长测量曲线诸如此类。为了隔离电路，从计算机测量也需要一个光电隔离接口。它可能永远不会发生，但如果它我会更新这个网页。

Last updated 4-september-2005.

TP1 RMS转换器 TP8
TP2 RMS转换器输入 TP9
TP3补偿网络的输入 TP10
TP4 A / D转换输入 TP11范围控制输入到A / D转换器TP5数字参考的A / D转换器的范围 TP12直流参考电压
TP6常见的 TP13使用- 01选项（电池充电电路）
有显示的段的BP－PIN和段PIN之间有个交流电压5V左右，没显示的段的BP－PIN和段之间没有电压；
芯片的驱动能力比较弱，最好给各段使用3极管（非门等）驱动，这样能显示亮一些。7-9 9.5伏 10-12 6.5伏