diff --git a/tcl/drivers/ah2550.tcl b/tcl/drivers/ah2550.tcl
new file mode 100644
index 0000000..4cdd9d2
--- /dev/null
+++ b/tcl/drivers/ah2550.tcl
@@ -0,0 +1,137 @@
+# Andeen Hagerling 2550 capacitance bridge 1kHz
+namespace eval ah2550 {} {
+}
+
+proc stdConfig::ah2550 {} {
+  controller std sendterminator=\r timeout=60 lineseparator=,
+
+  variable node
+  set node $node/tasks
+  prop start ah2550::start
+
+  obj ah2550 rd -none
+  prop read ah2550::read
+  prop do_read_avg 1
+  prop period 0
+  prop cnt 0
+
+  kids ah2550 {
+    node cap upd
+    prop fmt %.8f
+
+    node loss upd
+    prop fmt %.8f
+
+    node period out
+    default 5
+    prop check ah2550::change_period
+    prop write stdSct::complete
+
+    node  V out
+    prop label Exitation Voltage
+    prop writecmd "VO %g;SI"
+    prop complete ah2550::update
+
+    node average out -int
+    prop label "average setting"
+    prop writecmd "AV %d;SH AV"
+    prop complete ah2550::update_av
+  }
+}
+
+proc ah2550::start {} {
+  sct send "UN DF"
+  return ah2550::start1
+}
+
+proc ah2550::start1 {} {
+  set prefix [lindex [sct result] 0]
+  if {$prefix eq "UN"} { # this was the echo
+    sct send "SERIAL ECHO OFF"
+    return ah2550::start
+  }
+  if {$prefix ne "C=" && [sct result] ne "NO DATA FOUND"} {
+    error "bad response: [sct result]"
+  }
+  sct send "*IDN?"
+  return ah2550::start2
+}
+
+proc ah2550::start2 {} {
+  sct result [join [sct result]]
+  return stdSct::completeStart
+}
+
+proc ah2550::read {} {
+  sct send "SI"
+  sct sendtime [DoubleTime]
+  return ah2550::update
+}
+
+proc ah2550::update {} {
+  # analyze result: _ is a placeholder for text words
+  set res [string map {"," " , "} [sct result]]
+  set res [string map {"=" "= "} $res]
+  #clientput $res
+  lassign $res  prefix c _ _ _ l un _ _ v _ _ _ _ _ _ _
+  if {$prefix eq "SI"} {
+    sct send "\r\nSERIAL ECHO OFF\r"
+    return stdSct::complete
+  }
+  if {$prefix eq "C="} {
+    hupdate [sct objectPath]/status ""
+  } else {
+    hupdate [sct objectPath]/status [sct result]
+  }
+  set period [expr [DoubleTime] - [sct sendtime] + 0.1]
+  sct cnt [expr min(20, [sct cnt] + 1)]
+  set dif [expr $period - [sct period]]
+  sct period [expr [sct period] + $dif / [sct cnt]]
+  if {abs([sct period] - [hval [sct]/period]) > 0.1 || [sct cnt] == 10} {
+    set period [format {%.1f} [sct period]]
+    if {$period != [hval [sct]/period]} {
+      hupdate [sct]/period [format {%.1f} $period]
+      set_period [sct] $period
+      sct do_read_avg 1
+    }
+  }
+  hupdate [sct objectPath]/cap $c
+  hupdate [sct objectPath]/V $v
+  if {[string index $un 0] eq "Z"} {
+    sct send "ZERO OFF"
+    return ah2550::update
+  } elseif {[string index $un 0] eq "R"} {
+    sct send "REF OFF"
+    return ah2550::update
+  } elseif {$un ne "DF"} {
+    sct send "UN DF"
+    return ah2550::update
+  }
+  hupdate [sct objectPath]/loss $l
+  if {[sct do_read_avg]} {
+    sct do_read_avg 0
+    sct send "SH AV"
+    return ah2550::update_av
+  }
+  return idle
+}
+
+proc ah2550::update_av {} {
+  set res1 [lindex [split [sct result]  " "] end]
+  catch {
+    hupdate [sct objectPath]/average $res1
+  } msg
+  hsetprop [sct objectPath] cnt 0
+  return idle
+}
+
+proc ah2550::set_period {node target} {
+  [sct controllerName] poll $node $target
+  hupdate $node/period $target
+}
+
+proc ah2550::change_period {} {
+  set_period [sct objectPath] [sct target]
+  return idle
+}
+